Regioselectively substituted cellulose esters produced in a halogenated ionic liquid process and products produced therefrom

ABSTRACT

This invention relates to novel compositions comprising regioselectively substituted cellulose esters. One aspect of the invention relates to processes for preparing regioselectively substituted cellulose esters from cellulose dissolved in ionic liquids. Another aspect of the invention relates to the utility of regioselectively substituted cellulose esters in applications such as protective and compensation films for liquid crystalline displays.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. Non-Provisionalapplication Ser. No. 12/539,812 filed on Aug. 12, 2009, which is acontinuation in part application which claims priority to U.S.Non-Provisional application Ser. No. 12/189,415 filed Aug. 11, 2008,which claims priority to U.S. Provisional Application Ser. No.61/028,280; it also claims priority to U.S. Provisional Application61/088,423 filed Aug. 13, 2008, the disclosures of which are hereinincorporated by reference in their entirety to the extent they do notcontradict the statements herein.

BACKGROUND

1. Field of the Invention

The present invention relates generally to cellulose esters and/or ionicliquids. One aspect of the invention concerns processes for producingcellulose esters in ionic liquids.

2. Description of the Related Art

Cellulose is a β-1,4-linked polymer of anhydroglucose. Cellulose istypically a high molecular weight, polydisperse polymer that isinsoluble in water and virtually all common organic solvents. The use ofunmodified cellulose in wood or cotton products, such as in the housingor fabric industries, is well known. Unmodified cellulose is alsoutilized in a variety of other applications usually as a film (e.g.,cellophane), as a fiber (e.g., viscose rayon), or as a powder (e.g.,microcrystalline cellulose) used in pharmaceutical applications.Modified cellulose, including cellulose esters, are also utilized in awide variety of commercial applications. Cellulose esters can generallybe prepared by first converting cellulose to a cellulose triester, thenhydrolyzing the cellulose triester in an acidic aqueous media to thedesired degree of substitution (“DS”), which is the average number ofester substituents per anhydroglucose monomer. Hydrolysis of cellulosetriesters containing a single type of acyl substituent under theseconditions can yield a random copolymer that can consist of up to 8different monomers depending upon the final DS.

Ionic liquids (“ILs”) are liquids containing substantially only anionsand cations. Room temperature ionic liquids (“RTILs”) are ionic liquidsthat are in liquid form at standard temperature and pressure. Thecations associated with ILs are structurally diverse, but generallycontain one or more nitrogens that are part of a ring structure and canbe converted to a quaternary ammonium. Examples of these cations includepyridinum, pyridazinium, pyrimidinium, pyrazinium, imidazolium,pyrazolium, oxazolium, triazolium, thiazolium, piperidinium,pyrrolidinium, quinolinium, and isoquinolinium. The anions associatedwith ILs can also be structurally diverse and can have a significantimpact on the solubility of the ILs in different media. For example, ILscontaining hydrophobic anions such as hexafluorophosphates ortriflimides have very low solubilities in water while ILs containinghydrophilic anions such chloride or acetate are completely miscible inwater.

The names of ionic liquids can generally be abbreviated. Alkyl cationsare often named by the letters of the alkyl substituents and the cation,which are given within a set of brackets, followed by the abbreviationfor the anion. Although not expressively written, it should beunderstood that the cation has a positive charge and the anion has anegative charge. For example, [BMIm]OAc indicates1-butyl-3-methylimidazolium acetate, [AMIm]Cl indicates1-allyl-3-methylimidazolium chloride, and [EMIm]OF indicates1-ethyl-3-methylimidazolium formate.

Ionic liquids can be costly; thus, their use as solvents in manyprocesses may not be feasible. Despite this, methods and apparatus forreforming and/or recycling ionic liquids have heretofore beeninsufficient. Furthermore, many processes for producing ionic liquidsinvolve the use of halide and/or sulfur intermediates, or the use ofmetal oxide catalysts. Such processes can produce ionic liquids havinghigh levels of residual metals, sulfur, and/or halides.

SUMMARY OF THE INVENTION

In one embodiment of the invention, a process for making aregioselectively substituted cellulose ester is provided. The processcomprises:

(a) introducing a reaction medium comprising cellulose, a halide ionicliquid and a binary component into an esterification zone; and

(b) combining at least one acylating reagent with said reaction mediumin said esterification zone to esterify at least a portion of saidcellulose thereby producing said regioselectively substituted celluloseester; wherein said acylating reagent is added at one time or inconsecutive stages.

In another embodiment of the invention, a process for makingregioselectively substituted cellulose esters is provided. The processcomprises:

(a) dissolving a cellulose in a halide ionic liquid to thereby form aninitial cellulose solution;

(b) contacting said initial cellulose solution with a binary componentand an acylating reagent under conditions sufficient to provide anacylated cellulose solution comprising a cellulose ester; wherein saidacylating reagent is added at one time or in consecutive stages;

(c) contacting said acylated cellulose solution with a non-solvent tocause at least a portion of said cellulose ester to precipitate andthereby provide a slurry comprising precipitated cellulose ester and atleast a portion of said halide ionic liquid;

(d) separating at least a portion of said precipitated cellulose esterfrom said halide ionic liquid to thereby provide a recovered celluloseester and a separated halide ionic liquid; and

(e) optionally, recycling at least a portion of said separated halideionic liquid for use in dissolving additional cellulose

In another embodiment of the invention, photographic film, protectivefilm, or compensation film is provided.

In yet another embodiment of the invention, a compensation film isprovided comprising at least one regioselectively substituted celluloseester produced by the process discussed above wherein the compensationfilm has an Rth range from about −400 to about +100 nm.

In yet another embodiment, articles are provided comprising theregioselectively substituted cellulose ester produced by the processdiscussed above, such articles include, but are not limited to,thermoplastic molded products, coatings, personal care products, anddrug delivery products.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified diagram depicting the majors steps involved in aprocess for producing cellulose esters in ionic liquids;

FIG. 2 is a more detailed diagram of a process for producing celluloseesters, depicting a number of additional/optional steps for enhancing tooverall efficacy and/or efficiency of the process;

FIG. 3 is a plot of absorbance versus time showing the dissolution of 5weight percent cellulose in 1-butyl-3-methylimidazolium chloride;

FIG. 4 is a plot of absorbance versus time showing the acetylation ofcellulose dissolved in 1-butyl-3-methylimidazolium chloride with 5 molarequivalents of acetic anhydride;

FIG. 5 is a plot of absorbance versus time showing the dissolution of 5weight percent cellulose in 1-butyl-3-methylimidazolium chloride;

FIG. 6 is a plot of absorbance versus time showing the acetylation ofcellulose dissolved in 1-butyl-3-methylimidazolium chloride with 3 molarequivalents of acetic anhydride at 80° C.;

FIG. 7 is a plot of absorbance versus time showing the acetylation ofcellulose dissolved in 1-butyl-3-methylimidazolium chloride with 3 molarequivalents of acetic anhydride and 0.2 molar equivalents of methanesulfonic acid at 80° C.;

FIG. 8 is a plot of absorbance versus time showing the dissolution of 5weight percent cellulose in 1-butyl-3-methylimidazolium chloride;

FIG. 9 is a plot of absorbance versus time showing the acetylation ofcellulose dissolved in 1-butyl-3-methylimidazolium chloride with 3 molarequivalents of acetic anhydride and 0.2 molar equivalents of methanesulfonic acid at 80° C.;

FIG. 10 is a plot of absorbance versus time showing the dissolution of10 weight percent cellulose in 1-butyl-3-methylimidazolium chloride;

FIG. 11 is a plot of absorbance versus time showing the acetylation ofcellulose dissolved in 1-butyl-3-methylimidazolium chloride with 3 molarequivalents of acetic anhydride and 0.2 molar equivalents of methanesulfonic acid at 80° C.;

FIG. 12 is a plot of absorbance versus time showing the dissolution of15 weight percent cellulose in 1-butyl-3-methylimidazolium chloride;

FIG. 13 is a plot of absorbance versus time showing the acetylation ofcellulose dissolved in 1-butyl-3-methylimidazolium chloride with 3 molarequivalents of acetic anhydride and 0.2 molar equivalents of methanesulfonic acid at 100° C.;

FIG. 14 is a plot of absorbance versus time showing the dissolution of15 weight percent cellulose in 1-butyl-3-methylimidazolium chloride;

FIG. 15 is an NMR spectra showing the proton NMR spectra of a celluloseacetate prepared by direct acetylation;

FIG. 16 is plot of weight percent acetic acid versus time as determinedby infrared spectroscopy;

FIG. 17 is a plot of absorbance versus time showing the removal of waterfrom 1-butyl-3-methylimidazolium acetate prior to dissolution ofcellulose;

FIG. 18 is a plot of absorbance versus time showing the dissolution of10 weight percent cellulose in 1-butyl-3-methylimidazolium acetate atroom temperature;

FIG. 19 is a plot of absorbance versus time showing the acetylation ofcellulose dissolved in 1-butyl-3-methylimidazolium acetate with 5 molarequivalents of acetic anhydride and 0.1 molar equivalents of zincacetate;

FIG. 20 is a spectral analysis showing infrared spectra of1-butyl-3-methylimidazolium formate and 1-butyl-3-methylimidazoliumacetate, a spectrum after 0.5 molar equivalents of acetic anhydride hasbeen added to the 1-butyl-3-methylimidazolium formate, and a spectrumafter another 0.5 molar equivalents of acetic anhydride has been addedto the 1-butyl-3-methylimidazolium formate;

FIG. 21 is a plot of relative concentration versus time for1-butyl-3-methylimidazolium formate and 1-butyl-3-methylimidazoliumacetate upon first and second additions of 0.5 molar equivalents ofacetic anhydride;

FIG. 22 is spectral analysis showing infrared spectra of1-butyl-3-methylimidazolium formate, 1-butyl-3-methylimidazoliumformate, and a spectrum after 1 equivalent of acetic anhydride has beenadded to the 1-butyl-3-methylimidazolium formate in the presence of 2molar equivalents of methanol;

FIG. 23 is a plot of relative concentration versus time for1-butyl-3-methylimidazolium formate and 1-butyl-3-methylimidazoliumacetate upon addition of 2 molar equivalents of methanol and then uponaddition of 1 equivalent of acetic anhydride;

FIG. 24 is a plot of absorbance versus time showing the dissolution ofcellulose in 1-butyl-3-methylimidazolium acetate at 80° C.;

FIG. 25 is a plot of absorbance versus time showing the esterificationof cellulose dissolved in 1-butyl-3-methylimidazolium acetate;

FIG. 26 is a spectral analysis showing the ring proton resonances forcellulose acetates prepared from cellulose dissolved in1-butyl-3-methylimidazolium acetate (top spectrum), and the ring protonresonances for cellulose acetates prepared from cellulose dissolved in1-butyl-3-methylimidazolium chloride (bottom spectrum); and

FIG. 27 is a spectral analysis showing the ring proton resonances forcellulose acetates prepared from cellulose dissolved in1-butyl-3-methylimidazolium acetate after water addition (top spectrum)and before water addition (bottom spectrum).

FIG. 28 compares the viscosities of solutions of cellulose (5 wt %)dissolved in [BMIm]Cl, [BMIm]Cl+5 wt % acetic acid, and [BMIm]Cl+10 wt %acetic acid.

FIG. 29 compares the viscosities of solutions of cellulose contactmixtures without a cosolvent and with methyl ethyl ketone as acosolvent.

FIG. 30 shows a plot of absorbance for an infrared band at 1212 cm⁻¹(propionate ester and propionic acid) versus contact time duringesterification (3.7 eq propionic anhydride) of cellulose dissolvedeither in [BMIm]OPr or [BMIm]OPr+11.9 wt % propionic acid.

FIG. 31 shows a plot of absorbance versus time for a staged addition ofPr₂O (1^(st)) and Ac₂O (2^(nd)) illustrating the esterificationcellulose (1756, 1233, 1212 cm⁻¹), the consumption of anhydride (1815cm⁻¹), and the coproduction of carboxylic acid (1706 cm⁻¹) during theexperiment.

FIG. 32 shows the proton NMR spectra for the samples removed during thecontact period following the staged addition of Pr₂O (1^(st)) and Ac₂O(2^(nd)).

FIG. 33 shows the carbonyl region in the ¹³C NMR spectra of a samplefollowing the staged addition of Pr₂O (1^(st)) and Ac₂O (2^(nd)) [series1], following the staged addition of Ac₂O (1^(st)) and Pr₂O (2^(nd))[series 2], and following the mixed addition of Pr₂O and Ac₂O [series3].

FIG. 34 shows a plot of DS versus glass transition temperature (Tg) forthe cellulose acetate propionates prepared by staged addition of Pr₂O(1^(st)) and Ac₂O (2^(nd)) [series 1], by staged addition of Ac₂O(1^(st)) and Pr₂O (2^(nd)) [series 2], and by mixed addition of Pr₂O andAc₂O [series 3].

FIG. 35 shows a plot of DS propionate versus glass transitiontemperature (Tg) for the cellulose acetate propionates prepared bystaged addition of Pr₂O (1^(st)) and Ac₂O (2^(nd)) [series 1], by stagedaddition of Ac₂O (1^(st)) and Pr₂O (2^(nd)) [series 2], and by mixedaddition of Pr₂O and Ac₂O [series 3].

DETAILED DESCRIPTION

FIG. 1 depicts a simplified system for producing cellulose esters. Thesystem of FIG. 1 generally includes a dissolution zone 20, anesterification zone 40, a cellulose ester recovery/treatment zone 50,and an ionic liquid recovery/treatment zone 60.

As shown in FIG. 1, cellulose and an ionic liquid (“IL”) can be fed todissolution zone 20 via lines 62 and 64, respectively. In dissolutionzone 20, the cellulose can be dissolved to form an initial cellulosesolution comprising the cellulose and the ionic liquid. The initialcellulose solution can then be transported to esterification zone 40. Inesterification zone 40, a reaction medium comprising the dissolvedcellulose can be subjected to reaction conditions sufficient to at leastpartially esterify the cellulose, thereby producing an initial celluloseester. An acylating reagent can be added to esterification zone 40and/or dissolution zone 20 to help facilitate esterification of thedissolved cellulose in esterification zone 40.

As illustrated in FIG. 1, an esterified medium can be withdrawn fromesterification zone 40 via line 80 and thereafter transported tocellulose ester recovery/treatment zone 50 where the initial celluloseester can be recovered and treated to thereby produce a final celluloseester that exits recovery/treatment zone 50 via line 90. A recyclestream is produced from cellulose ester recovery/treatment zone 50 vialine 86. This recycle stream can comprise an altered ionic liquidderived from the ionic liquid originally introduced into dissolutionzone 20. The recycle stream in line 86 can also include various othercompounds including byproducts of reactions occurring in upstream zones20,40,50 or additives employed in upstream zones 20,40,50. The recyclestream in line 86 can be introduced into ionic liquid recovery/treatmentzone 60 where it can be subjected to separation and/or reformationprocesses. A recycled ionic liquid can be produced from ionic liquidrecovery/treatment zone 60 and can be routed back to dissolution zone 20via line 70. Additional details of the streams, reactions, and stepsinvolved in the cellulose ester production system of FIG. 1 are providedimmediately below.

The cellulose fed to dissolution zone 20 via line 62 can be anycellulose known in the art that is suitable for use in the production ofcellulose esters. In one embodiment, the cellulose suitable for use inthe present invention can be obtained from soft or hard woods in theform of wood pulps, or from annual plants such as cotton or corn. Thecellulose can be a β-1,4-linked polymer comprising a plurality ofanhydroglucose monomer units. The cellulose suitable for use in thepresent invention can generally comprise the following structure:

Additionally, the cellulose employed in the present invention can havean α-cellulose content of at least about 90 percent by weight, at leastabout 95 percent by weight, or at least 98 percent by weight.

The cellulose fed to dissolution zone 20 via line 62 can have a degreeof polymerization (“DP”) of at least about 10, at least about 250, atleast about 1,000, or at least 5,000. As used herein, the term “degreeof polymerization,” when referring to cellulose and/or cellulose esters,shall denote the average number of anhydroglucose monomer units percellulose polymer chain. Furthermore, the cellulose can have a weightaverage molecular weight in the range of from about 1,500 to about850,000, in the range of from about 40,000 to about 200,000, or in therange of from 55,000 to about 160,000. Additionally, the cellulosesuitable for use in the present invention can be in the form of a sheet,a hammer milled sheet, fiber, or powder. In one embodiment, thecellulose can be a powder having an average particle size of less thanabout 500 micrometers (“μm”), less than about 400 μm, or less than 300μm.

The ionic liquid fed to dissolution zone 20 via line 64 can be any ionicliquid capable of at least partially dissolving cellulose. As usedherein, the term “ionic liquid” shall denote any substance containingsubstantially only ions, and which has a melting point at a temperatureof 200° C. or less. In one embodiment, the ionic liquid suitable for usein the present invention can be a cellulose dissolving ionic liquid. Asused herein, the term “cellulose dissolving ionic liquid” shall denoteany ionic liquid capable of dissolving cellulose in an amount sufficientto create an at least 0.1 weight percent cellulose solution. In oneembodiment, the ionic liquid fed to dissolution zone 20 via line 64 canhave a temperature at least 10° C. above the melting point of the ionicliquid. In another embodiment, the ionic liquid can have a temperaturein the range of from about 0 to about 100° C., in the range of fromabout 20 to about 80° C., or in the range of from 25 to 50° C.

In one embodiment, the ionic liquid fed to dissolution zone 20 via line64 can comprise water, nitrogen-containing bases, alcohol, or carboxylicacid. The ionic liquid in line 64 can comprise less than about 15 weightpercent of each of water, nitrogen-containing bases, alcohol, andcarboxylic acid; less than about 5 weight percent of each of water,nitrogen-containing bases, alcohol, and carboxylic acid; or less than 2weight percent of each of water, nitrogen-containing bases, alcohol, andcarboxylic acid.

As mentioned above, an ionic liquid comprises ions. These ions includeboth cations (i.e., positively charged ions) and anions (i.e.,negatively charged ions). In one embodiment, the cations of the ionicliquid suitable for use in the present invention can include, but arenot limited to, imidazolium, pyrazolium, oxazolium, 1,2,4-triazolium,1,2,3-triazolium, and/or thiazolium cations, which correspond to thefollowing structures:

In the above structures, R₁ and R₂ can independently be a C₁ to C₈ alkylgroup, a C₂ to C₈ alkenyl group, or a C₁ to C₈ alkoxyalkyl group. R₃,R₄, and R₅ can independently be a hydrido, a C₁ to C₈ alkyl group, a C₂to C₈ alkenyl group, a C₁ to C₈ alkoxyalkyl group, or a C₁ to C₈ alkoxygroup. In one embodiment, the cation of the ionic liquid used in thepresent invention can comprise an alkyl substituted imidazolium cation,where R₁ is a C₁ to C₄ alkyl group, and R₂ is a different C₁ to C₄ alkylgroup.

In one embodiment of the present invention, the cellulose dissolvingionic liquid can be a carboxylated ionic liquid. As used herein, theterm “carboxylated ionic liquid” shall denote any ionic liquidcomprising one or more carboxylate anions. Carboxylate anions suitablefor use in the carboxylated ionic liquids of the present inventioninclude, but are not limited to, C₁ to C₂₀ straight- or branched-chaincarboxylate or substituted carboxylate anions. Examples of suitablecarboxylate anions for use in the carboxylated ionic liquid include, butare not limited to, formate, acetate, propionate, butyrate, valerate,hexanoate, lactate, oxalate, or chloro-, bromo-, fluoro-substitutedacetate, propionate, or butyrate and the like. In one embodiment, theanion of the carboxylated ionic liquid can be a C₂ to C₆ straight-chaincarboxylate. Furthermore, the anion can be acetate, propionate,butyrate, or a mixture of acetate, propionate, and/or butyrate.

Examples of carboxylated ionic liquids suitable for use in the presentinvention include, but are not limited to, 1-ethyl-3-methylimidazoliumacetate, 1-ethyl-3-methylimidazolium propionate,1-ethyl-3-methylimidazolium butyrate, 1-butyl-3-methylimidazoliumacetate, 1-butyl-3-methylimidazolium propionate,1-butyl-3-methylimidazolium butyrate, or mixtures thereof.

In one embodiment of the present invention, the carboxylated ionicliquid can contain sulfur in an amount less than 200 parts per millionby weight (“ppmw”), less than 100 ppmw, less than 50 ppmw, or less than10 ppmw based on the total ion content of the carboxylated ionic liquid.Additionally, the carboxylated ionic liquid can contain a total halidecontent of less than 200 ppmw, less than 100 ppmw, less than 50 ppmw, orless than 10 ppmw based on the total ion content of the carboxylatedionic liquid. Furthermore, the carboxylated ionic liquid can contain atotal metal content of less than 200 ppmw, less than 100 ppmw, less than50 ppmw, or less than 10 ppmw based on the total ion content of thecarboxylated ionic liquid. In one embodiment, carboxylated ionic liquidcan contain transition metals in an amount less than 200 ppmw, less than100 ppmw, less than 50 ppmw, or less than 10 ppmw. Sulfur, halide, andmetal content of the carboxylated ionic liquid can be determined byx-ray fluorescence (“XRF”) spectroscopy.

The carboxylated ionic liquid of the present invention can be formed byany process known in the art for making ionic liquids having at leastone carboxylate anion. In one embodiment, the carboxylated ionic liquidof the present invention can be formed by first forming an intermediateionic liquid. The intermediate ionic liquid can be any known ionicliquid that can participate in an anion exchange reaction.

In one embodiment, the intermediate ionic liquid can comprise aplurality of cations such as, for example, imidazolium, pyrazolium,oxazolium, 1,2,4-triazolium, 1,2,3-triazolium, and/or thiazoliumcations, which correspond to the following structures:

In the above structures, R₁ and R₂ can independently be a C₁ to C₈ alkylgroup, a C₂ to C₈ alkenyl group, or a C₁ to C₈ alkoxyalkyl group. R₃,R₄, and R₅ can independently be a hydrido, a C₁ to C₈ alkyl group, a C₂to C₈ alkenyl group, a C₁ to C₈ alkoxyalkyl group, or a C₁ to C₈ alkoxygroup. In one embodiment, the cation of the intermediate ionic liquidused in the present invention can comprise an alkyl substitutedimidazolium cation, where R₁ is a C₁ to C₄ alkyl group, and R₂ is adifferent C₁ to C₄ alkyl group. In one embodiment, the cation of theintermediate ionic liquid can comprise 1-ethyl-3-methylimidazolium or1-butyl-3-methylimidazolium.

Additionally, the intermediate ionic liquid can comprise a plurality ofanions. In one embodiment, the intermediate ionic liquid can comprise aplurality of carboxylate anions, such as, for example, formate, acetate,and/or propionate anions.

In one embodiment, the intermediate ionic liquid can comprise an alkylamine formate. The amine cation of the alkyl amine formate can compriseany of the above-described substituted or unsubstituted imidazolium,pyrazolium, oxazolium, 1,2,4-triazolium, 1,2,3-triazolium, and/orthiazolium cations. In one embodiment, the amine of the alkyl amineformate can be an alkyl substituted imidazolium, alkyl substitutedpyrazolium, alkyl substituted oxazolium, alkyl substituted triazolium,alkyl substituted thiazolium, and mixtures thereof. In one embodiment,the amine of the alkyl amine formate can be an alkyl substitutedimidazolium. Examples of alkyl amine formates suitable for use in thepresent invention include, but are not limited to,1-methyl-3-methylimidazolium formate, 1-ethyl-3-methylimidazoliumformate, 1-propyl-3-methylimidazolium formate,1-butyl-3-methylimidazolium formate, 1-pentyl-3-methylimidazoliumformate, and/or 1-octyl-3-methylimidazolium formate.

The intermediate ionic liquid useful in the present invention can beformed by contacting at least one amine with at least one alkyl formate.Amines suitable for use in the present invention include, but are notlimited to, substituted or unsubstituted imidazoles, pyrazoles,oxazoles, triazoles, and/or thiazoles. In one embodiment, the alkylamine formate can be formed by contacting at least one alkyl substitutedimidazole with at least one alkyl formate. Examples of alkyl substitutedimidazoles suitable for use in forming the intermediate ionic liquidinclude, but are not limited to, 1-methylimidazole, 1-ethylimidazole,1-propylimidazole, 1-butylimidazole, 1-hexylimidazole, and/or1-octylimidazole. Examples of alkyl formates suitable for use in formingthe intermediate ionic liquid include, but are not limited to, methylformate, ethyl formate, propyl formate, isopropyl formate, butylformate, isobutyl formate, tert-butyl formate, hexyl formate, octylformate, and the like. In one embodiment, the alkyl formate used informing the intermediate ionic liquid can comprise methyl formate.

Once the intermediate ionic liquid has been formed, the intermediateionic liquid can be contacted with one or more carboxylate anion donorsat a contact time, pressure, and temperature sufficient to cause the atleast partial conversion of the intermediate ionic liquid to at leastone of the above-mentioned carboxylated ionic liquids. Suchinterconversion can be accomplished via anion exchange between thecarboxylate anion donor and the intermediate ionic liquid. In oneembodiment, at least a portion of the formate of the alkyl amine formatecan be replaced via anion exchange with a carboxylate anion originatingfrom one or more carboxylate anion donors.

Carboxylate anion donors useful in the present invention can include anysubstance capable of donating at least one carboxylate anion. Examplesof carboxylate anion donors suitable for use in the present inventioninclude, but are not limited to, carboxylic acids, anhydrides, and/oralkyl carboxylates. In one embodiment, the carboxylate anion donor cancomprise one or more C₂ to C₂₀ straight- or branched-chain alkyl or arylcarboxylic acids, anhydrides, or methyl esters. Additionally, thecarboxylate anion donor can comprise one or more C₂ to C₁₂straight-chain alkyl carboxylic acids, anhydrides, or methyl esters.Furthermore, the carboxylate anion donor can comprise one or more C₂ toC₄ straight-chain alkyl carboxylic acids, anhydrides, or methyl esters.In one embodiment, the carboxylate anion donor can comprise at least oneanhydride, which can comprise acetic anhydride, propionic anhydride,butyric anhydride, isobutyric anhydride, valeric anhydride, hexanoicanhydride, 2-ethylhexanoic anhydride, nonanoic anhydride, lauricanhydride, palmitic anhydride, stearic anhydride, benzoic anhydride,substituted benzoic anhydrides, phthalic anhydride, isophthalicanhydride, and mixtures thereof.

The amount of carboxylate anion donor useful in the present inventioncan be any amount suitable to convert at least a portion of theintermediate ionic liquid to a carboxylated ionic liquid. In oneembodiment, the carboxylate anion donor can be present in a molar ratiowith the intermediate ionic liquid in the range of from about 1:1 toabout 20:1 carboxylate anion donor-to-intermediate ionic liquid anioncontent, or in the range of from 1:1 to 6:1 carboxylate aniondonor-to-intermediate ionic liquid anion content. In one embodiment,when alkyl amine formate is present as the intermediate ionic liquids,the carboxylate anion donor can be present in an amount in the range offrom 1 to 20 molar equivalents per alkyl amine formate, or in the rangeof from 1 to 6 molar equivalents per alkyl amine formate.

The anion exchange between the intermediate ionic liquid and thecarboxylate anion donor can be accomplished in the presence of at leastone alcohol. Alcohols useful in the present invention include, but arenot limited to, alkyl or aryl alcohols such as methanol, ethanol,n-propanol, i-propanol, n-butanol, i-butanol, t-butanol, phenol, and thelike. In one embodiment, the alcohol can be methanol. The amount ofalcohol present in the contact mixture during interconversion of theintermediate ionic liquid can be in the range of from about 0.01 toabout 20 molar equivalents of the ionic liquid, or in the range of from1 to 10 molar equivalents of the ionic liquid.

In one embodiment, water can be present in the contact mixture duringthe anion exchange between the intermediate ionic liquid and thecarboxylate anion donor. The amount of water present in the contactmixture during interconversion of the intermediate ionic liquid can bein the range of from about 0.01 to about 20 molar equivalents of theionic liquid, or in the range of from 1 to 10 molar equivalents of theionic liquid.

As mentioned above, the interconversion of the intermediate ionic liquidto the carboxylated ionic liquid can be performed at a contact time,pressure, and temperature sufficient to cause the at least partialconversion of the intermediate ionic liquid to the carboxylated ionicliquid. In one embodiment, the interconversion can be performed for atime in the range of from about 1 minute to about 24 hours, or in therange of from 30 minutes to 18 hours. Additionally, the interconversioncan be performed at a pressure up to 21,000 kPa, or up to 10,000 kPa. Inone embodiment, the interconversion can be performed at a pressure inthe range of from about 100 to about 21,000 kPa, or in the range of from100 to 10,000 kPa. Furthermore, the interconversion can be performed ata temperature in the range of from about 0 to about 200° C., or in therange of from 25 to 170° C.

In one embodiment, the resulting carboxylated ionic liquid can comprisecarboxylate anions comprising substituted or non-substituted C₁ to C₂₀straight- or branched-chain carboxylate anions. In one embodiment, thecarboxylate anion can comprise a C₂ to C₆ straight-chain carboxylateanion. Additionally, the carboxylated ionic liquid can comprisecarboxylate anions such as, for example, formate, acetate, propionate,butyrate, valerate, hexanoate, lactate, and/or oxalate. In oneembodiment, the carboxylated ionic liquid can comprise at least 50percent carboxylate anions, at least 70 percent carboxylate anions, orat least 90 percent carboxylate anions. In another embodiment, thecarboxylated ionic liquid can comprise at least 50 percent acetateanions, at least 70 percent acetate anions, or at least 90 percentacetate anions.

In an alternative embodiment of the present invention, theabove-mentioned cellulose dissolving ionic liquid can be a halide ionicliquid. As used herein, the term “halide ionic liquid” shall denote anyionic liquid that contains at least one halide anion. In one embodiment,the halide anion of the halide ionic liquid can be fluoride, chloride,bromide, and/or iodide. In another embodiment, the halide anion can bechloride and/or bromide. Additionally, as mentioned above, the cation ofthe cellulose dissolving ionic liquid can comprise, but is not limitedto, imidazolium, pyrazolium, oxazolium, 1,2,4-triazolium,1,2,3-triazolium, and/or thiazolium cations. Any method known in the artsuitable for making a halide ionic liquid can be employed in the presentinvention.

Examples of halide ionic liquids suitable for use in the presentinvention include, but are not limited to, 1-butyl-3-methylimidazoliumchloride, 1-propyl-3-methylimidazolium chloride,1-ethyl-3-methylimidazolium chloride, 1-allyl-3-methylimidazoliumchloride, or mixtures thereof.

Referring again to FIG. 1, the weight percent of the amount of cellulosefed to dissolution zone 20 to the cumulative amount of ionic liquid(including recycled ionic liquid) fed to dissolution zone 20 can be inthe range of from about 1 to about 40 weight percent, in the range offrom about 5 to about 25 weight percent, or in the range of from 10 to20 weight percent based on the combined weight of cellulose and ionicliquid. In one embodiment, the resulting medium formed in dissolutionzone 20 can comprise other components, such as, for example, water,alcohol, acylating reagent, and/or carboxylic acids. In one embodiment,the medium formed in dissolution zone 20 can comprise water in an amountin the range of from about 0.001 to about 200 weight percent, in therange of from about 1 to about 100 weight percent, or in the range offrom 5 to 15 weight percent based on the entire weight of the medium.Additionally, the medium formed in dissolution zone 20 can comprise acombined concentration of alcohol in an amount in the range of fromabout 0.001 to about 200 weight percent, in the range of from about 1 toabout 100 weight percent, or in the range of from 5 to 15 weight percentbased on the entire weight of the medium.

The medium formed in dissolution zone 20 can optionally comprise one ormore carboxylic acids. The medium formed in dissolution zone 20 cancomprise a total concentration of carboxylic acids in the range of fromabout 0.01 to about 25 weight percent, in the range of from about 0.05to about 15 weight percent, or in the range of from 0.1 to 5 weightpercent based on the total concentration of ionic liquid in the mediumformed in dissolution zone 20. Examples of suitable carboxylic acidsuseful in this embodiment include, but are not limited to, acetic acid,propionic acid, butyric acid, isobutyric acid, valeric acid, hexanoicacid, 2-ethylhexanoic acid, nonanoic acid, lauric acid, palmitic acid,stearic acid, benzoic acid, substituted benzoic acids, phthalic acid,and isophthalic acid. In one embodiment, the carboxylic acid in themedium formed in dissolution zone 20 can comprise acetic acid, propionicacid, and/or butyric acid.

As is described in more detail below with reference to FIG. 2, at leasta portion of the carboxylic acids present in the medium formed indissolution zone 20 can originate from a recycled carboxylated ionicliquid introduced via line 70. Though not wishing to be bound by theory,the inventors have unexpectedly found that the use of carboxylic acid inthe medium formed in dissolution zone 20 can reduce the viscosity of thecellulose/ionic liquid solution, thereby enabling easier processing ofthe solution. Additionally, the presence of carboxylic acid in themedium in dissolution zone 20 appears to reduce the melting points ofthe ionic liquids employed, thereby allowing processing of the ionicliquids at lower temperatures than predicted.

The medium formed in dissolution zone 20 can optionally comprise anacylating reagent, as is discussed in more detail below. The optionalacylating reagent can be introduced into dissolution zone 20 via line78. In one embodiment, the medium formed in dissolution zone 20 cancomprise acylating reagent in an amount in the range of from about 0.01molar equivalents to about 20 molar equivalents, in the range of fromabout 0.5 molar equivalents to about 10 molar equivalents, or in therange of from 1.8 molar equivalents to about 4 molar equivalents basedon the total amount of cellulose in the medium in dissolution zone 20.

The medium formed in dissolution zone 20 can also comprise recycledionic liquid, as is discussed in more detail below with reference toFIG. 2. The recycled ionic liquid can be introduced into dissolutionzone 20 via line 70. The medium formed in dissolution zone 20 cancomprise recycled ionic liquid in an amount in the range of from about0.01 to about 99.99 weight percent, in the range of from about 10 toabout 99 weight percent, or in the range of from 90 to 98 weight percentbased on the total amount of ionic liquid in dissolution zone 20.

In one embodiment, the medium can optionally comprise immiscible orsubstantially immiscible co-solvents. Such co-solvents can comprise oneor more co-solvents that are immiscible or sparingly soluble with thecellulose-ionic liquid mixture. Surprisingly, the addition of animmiscible or sparingly soluble co-solvent does not cause precipitationof the cellulose upon contacting the cellulose-ionic liquid mixture.However, upon contact with an acylating reagent, as will be discussed inmore detail below, the cellulose can be esterified which can change thesolubility of the now cellulose ester-ionic liquid solution with respectto the formerly immiscible or sparingly soluble co-solvent. Accordingly,subsequent to esterification, the contact mixture can become a singlephase or highly dispersed mixture of cellulose ester-ionic liquid in theco-solvent. The resulting single phase or dispersed phase has much lowersolution viscosity than the initial cellulose-ionic liquid solution.

This discovery is significant in that heretofore highly viscouscellulose solutions can now be used to make cellulose esters while stillmaintaining the ability to mix and process the solution. The discoveryalso provides a viable method to process highly viscous cellulose-ionicliquid solutions at lower contact temperatures.

Immiscible or sparingly soluble co-solvents suitable for use in thepresent invention can comprise alkyl or aryl esters, ketones, alkylhalides, hydrophobic ionic liquids, and the like. Specific examples ofimmiscible or sparingly soluble co-solvents include, but are not limitedto, methyl acetate, ethyl acetate, isopropyl acetate, methyl propionate,methyl butyrate, acetone, methyl ethyl ketone, chloroform, methylenechloride, alkyl immidazolium hexafluorophosphate, alkyl immidazoliumtriflimide, and the like. In one embodiment, the immiscible or sparinglysoluble co-solvents can comprise methyl acetate, methyl propionate,methyl butyrate, methyl ethyl ketone, and/or methylene chloride. Theweight ratio of immiscible or sparingly soluble co-solvents tocellulose-ionic liquid mixture can be in the range of from about 1:20 toabout 20:1. or in the range of from 1:5 to 5:1.

In one embodiment, the cellulose entering dissolution zone 20 via line62 can initially be dispersed in the ionic liquid. Dispersion of thecellulose in the ionic liquid can be achieved by any mixing means knownin the art. In one embodiment, dispersion of the cellulose can beachieved by mechanical mixing, such as mixing by one or more mechanicalhomogenizers.

After the cellulose has been dispersed in the ionic liquid, dissolutionof the cellulose in dissolution zone 20, along with removal of at leasta portion of any volatile components in the mixture, can be achievedusing any method known in the art. For example, dissolution of thecellulose can be achieved by lowering the pressure and/or raising thetemperature of the cellulose/ionic liquid dispersion initially formed indissolution zone 20. Accordingly, after the cellulose is dispersed inthe ionic liquid, the pressure can be lowered in dissolution zone 20. Inone embodiment, the pressure in dissolution zone 20 can be lowered toless than about 100 millimeters mercury (“mm Hg”), or less than 50 mmHg. Additionally, the cellulose/ionic liquid dispersion can be heated toa temperature in the range of from about 60 to about 100° C., or in therange of from 70 to about 85° C. After dissolution, the resultingsolution can be maintained at the above-described temperatures andpressures for a time in the range of from about 0 to about 100 hours, orin the range of from about 1 to about 4 hours. The cellulose solutionformed in dissolution zone 20 can comprise cellulose in an amount in therange of from about 1 to about 40 weight percent, or in the range offrom 5 to 20 weight percent, based on the entire weight of the solution.In another embodiment, the cellulose solution formed in dissolution zone20 can comprise dissolved cellulose in an amount of at least 10 weightpercent based on the entire weight of the solution.

After dissolution, at least a portion of the resulting cellulosesolution can be removed from dissolution zone 20 via line 66 and routedto esterification zone 40. In one embodiment, at least one acylatingreagent can be introduced into esterification zone 40 to esterify atleast a portion of the cellulose. As mentioned above, in anotherembodiment, at least one acylating reagent can be introduced intodissolution zone 20. Additionally, the acylating reagent can be addedafter the cellulose has been dissolved in the ionic liquid. Optionally,at least a portion of the acylating reagent can be added to the ionicliquids prior to dissolution of the cellulose in the ionic liquid.Regardless of where the acylating reagent is added, at least a portionof the cellulose in esterification zone 40 can undergo esterificationsubsequent to being contacted with the acylating reagent.

As used herein, the term “acylating reagent” shall denote any chemicalcompound capable of donating at least one acyl group to a cellulose. Asused herein, the term “acyl group” shall denote any organic radicalderived from an organic acid by the removal of a hydroxyl group.Acylating reagents useful in the present invention can be one or moreC_(i) to C₂₀ straight- or branched-chain alkyl or aryl carboxylicanhydrides, carboxylic acid halides, diketene, or acetoacetic acidesters. Examples of carboxylic anhydrides suitable for use as acylatingreagents in the present invention include, but are not limited to,acetic anhydride, propionic anhydride, butyric anhydride, isobutyricanhydride, valeric anhydride, hexanoic anhydride, 2-ethylhexanoicanhydride, nonanoic anhydride, lauric anhydride, palmitic anhydride,stearic anhydride, benzoic anhydride, substituted benzoic anhydrides,phthalic anhydride, and isophthalic anhydride. Examples of carboxylicacid halides suitable for use as acylating reagents in the presentinvention include, but are not limited to, acetyl, propionyl, butyryl,hexanoyl, 2-ethylhexanoyl, lauroyl, palmitoyl, benzoyl, substitutedbenzoyl, and stearoyl chlorides. Examples of acetoacetic acid esterssuitable for use as acylating reagents in the present invention include,but are not limited to, methyl acetoacetate, ethyl acetoacetate, propylacetoacetate, butyl acetoacetate, and tert-butyl acetoacetate. In oneembodiment, the acylating reagents can be C₂ to C₉ straight- orbranched-chain alkyl carboxylic anhydrides selected from the groupconsisting of acetic anhydride, propionic anhydride, butyric anhydride,2-ethylhexanoic anhydride, and nonanoic anhydride.

The reaction medium formed in esterification zone 40 can comprisecellulose in an amount in the range of from about 1 to about 40 weightpercent, in the range of from about 5 to about 25 weight percent, or inthe range of from 10 to 20 weight percent, based on the weight of theionic liquid in the reaction medium. Additionally, the reaction mediumformed in esterification zone 40 can comprise ionic liquid in an amountin the range of from about 20 to about 98 weight percent, in the rangeof from about 30 to about 95 weight percent, or in the range of from 50to 90 weight percent based on the total weight of the reaction medium.Furthermore, the reaction medium formed in esterification zone 40 cancomprise acylating reagent in an amount in the range of from about 1 toabout 50 weight percent, in the range of from about 5 to about 30 weightpercent, or in the range of from 10 to 20 weight percent based on thetotal weight of the reaction medium. Furthermore, the reaction mediumformed in esterification zone 40 can have a cumulative concentration ofnitrogen containing bases and carboxylic acids in an amount less than 15weight percent, less than 5 weight percent, or less than 2 weightpercent.

In one embodiment, the weight ratio of cellulose-to-acylating reagent inesterification zone 40 can be in the range of from about 90:10 to about10:90, in the range of from about 60:40 to about 25:75, or in the rangeof from 45:55 to 35:65. In one embodiment, the acylating reagent can bepresent in esterification zone 40 in an amount less than 5, less than 4,less than 3, or less than 2.7 molar equivalents per anhydroglucose unit.

In one embodiment of the present invention, when a halide ionic liquidis employed as the cellulose dissolving ionic liquid, a limited excessof acylating reagent can be employed in the esterification of thecellulose to achieve a cellulose ester with a particular DS. Thus, inone embodiment, less than 20 percent molar excess, less than 10 percentmolar excess, less than 5 percent molar excess, or less than 1 percentexcess of acylating reagent can be employed during esterification.

In a preferred embodiment of the present invention when 2 or moreacylating reagents are employed in the esterification of cellulose, the2 or more acylating reagents can be added as a mixture or the additioncan be staged. In a staged addition, the acylating reagents are addedconsecutively. Preferably, in a staged addition at least about 80 molarpercent of the first acylating reagent is allowed to react with thecellulose prior to adding the next acylating reagent.

Optionally, one or more catalysts can be introduced into esterificationzone 40 to aid in esterification of the cellulose. The catalyst employedin the present invention can be any catalyst that increases the rate ofesterification in esterification zone 40. Examples of catalysts suitablefor use in the present invention include, but are not limited to, proticacids of the type sulfuric acid, alkyl sulfonic acids, aryl sulfonicacids, functional ionic liquids, and weak Lewis acids of the type MXn,where M is a transition metal exemplified by B, Al, Fe, Ga, Sb, Sn, As,Zn, Mg, or Hg, and X is halogen, carboxylate, sulfonate, alkoxide,alkyl, or aryl. In one embodiment, the catalyst is a protic acid. Theprotic acid catalysts can have a pKa in the range of from about −5 toabout 10, or in the range of from −2.5 to 2.0. Examples of suitableprotic acid catalysts include methane sulfonic acid (“MSA”), p-toluenesulfonic acid, and the like. In one embodiment, the one or morecatalysts can be Lewis acids. Examples of Lewis acids suitable for useas catalysts include ZnCl2, Zn(OAc)2, and the like. When a catalyst isemployed, the catalyst can be added to the cellulose solution prior toadding the acylating reagent. In another embodiment the catalyst can beadded to the cellulose solution as a mixture with the acylating reagent.

Additionally, functional ionic liquids can be employed as catalystsduring esterification of the cellulose. Functional ionic liquids areionic liquids containing specific functional groups, such as hydrogensulfonate, alkyl or aryl sulfonates, and carboxylates, that effectivelycatalyze the esterification of cellulose by the acylating reagent.Examples of functional ionic liquids include 1-alkyl-3-methylimidazoliumhydrogen sulfate, methyl sulfonate, tosylate, and trifluoroacetate,where the alkyl can be a C₁ to C₁₀ straight-chain alkyl group.Additionally, suitable functional ionic liquids for use in the presentinvention are those in which the functional group is covalently linkedto the cation. Thus, functional ionic liquids can be ionic liquidscontaining functional groups, and are capable of catalyzing theesterification of cellulose with an acylating reagent.

An example of a covalently-linked functional ionic liquid suitable foruse in the present invention includes, but is not limited to, thefollowing structure:

where at least one of the R₁, R₂, R₃, R₄, R₅ groups are replaced withthe group (CHX)_(n)Y, where X is hydrogen or halide, n is an integer inthe range of from 1 to 10, and Y is sulfonic or carboxylate and theremainder R₁, R₂, R₃, R₄, R₅ groups are those previously described inrelation to the cations suitable for use as the cellulose dissolvingionic liquid. Examples of cations suitable for use in the functionalionic liquids to be used in the present invention include, but are notlimited to, 1-alkyl-3-(1-carboxy-2,2-difluoroethyl)imidazolium,1-alkyl-3-(1-carboxy-2,2-difluoropropyl)imidazolium,1-alkyl-3-(1-carboxy-2,2-difluoro-butyl)imidazolium,1-alkyl-3-(1-carboxy-2,2-difluorohexyl)imidazolium,1-alkyl-3-(1-sulfonylethyl)imidazolium,1-alkyl-3-(1-sulfonylpropyl)imidazolium,1-alkyl-3-(1-sulfonylbutyl)imidazolium, and1-alkyl-3-(1-sulfonylhexyl)imidazolium, where the alkyl can be a C₁ toC₁₀ straight-chain alkyl group.

The amount of catalyst used to catalyze the esterification of cellulosemay vary depending upon the type of catalyst employed, the type ofacylating reagent employed, the type of ionic liquid, the contacttemperature, and the contact time. Thus, a broad concentration ofcatalyst employed is contemplated by the present invention. In oneembodiment, the amount of catalyst employed in esterification zone 40can be in the range of from about 0.01 to about 30 mol percent catalystper anhydroglucose unit (“AGU”), in the range of from about 0.05 toabout 10 mol percent catalyst per AGU, or in the range of from 0.1 to 5mol percent catalyst per AGU. In one embodiment, the amount of catalystemployed can be less than 30 mol percent catalyst per AGU, less than 10mol percent catalyst per AGU, less than 5 mol percent catalyst per AGU,or less than 1 mol percent catalyst per AGU. In another embodiment, whena catalyst is employed as a binary component, the amount of binarycomponent employed can be in the range of from about 0.01 to about 100mol percent per AGU, in the range of from about 0.05 to about 20 molpercent per AGU, or in the range of from 0.1 to 5 mol percent per AGU.

The inventors have discovered a number of surprising and unpredictableadvantages apparently associated with employing a catalyst as a binarycomponent during the esterification of cellulose. For example, theinventors have discovered that the inclusion of a binary component canaccelerate the rate of esterification. Very surprisingly, the binarycomponent can also serve to improve solution and product color, preventgellation of the esterification mixture, provide increased DS values inrelation to the amount of acylating reagent employed, and/or help todecrease the molecular weight of the cellulose ester product. Though notwishing to be bound by theory, it is believed that the use of a binarycomponent acts to change the network structure of the ionic liquidcontaining the dissolved cellulose ester. This change in networkstructure may lead to the observed surprising and unpredicted advantagesof using the binary component.

As mentioned above, at least a portion of the cellulose can undergo anesterification reaction in esterification zone 40. The esterificationreaction carried out in esterification zone 40 can operate to convert atleast a portion of the hydroxyl groups contained on the cellulose toester groups, thereby forming a cellulose ester. As used herein, theterm “cellulose ester” shall denote a cellulose polymer having at leastone ester substituent. Furthermore, the term “mixed cellulose ester”shall denote a cellulose ester having at least two different estersubstituents on a single cellulose ester polymer chain. In oneembodiment, at least a portion of the ester groups on the resultingcellulose ester can originate from the above-described acylatingreagent. The cellulose esters thus prepared can comprise the followingstructure:

where R₂, R₃, and R₆ can independently be hydrogen, so long as R₂, R₃,and R₆ are not all hydrogen simultaneously, or a C₁ to C₂₀ straight- orbranched-chain alkyl or aryl groups bound to the cellulose via an esterlinkage.

In one embodiment, when the ionic liquid employed is a carboxylatedionic liquid, one or more of the ester groups on the resulting celluloseester can originate from the ionic liquid in which the cellulose isdissolved. The amount of ester groups on the resulting cellulose esterthat originate from the carboxylated ionic liquid can be at least 10percent, at least 25 percent, at least 50 percent, or at least 75percent.

Additionally, the ester group on the cellulose ester originating fromthe carboxylated ionic liquid can be a different ester group than theester group on the cellulose ester that originates from the acylatingreagent. Though not wishing to be bound by theory, it is believed thatwhen an acylating reagent is introduced into a carboxylated ionicliquid, an anion exchange can occur such that a carboxylate ionoriginating from the acylating reagent replaces at least a portion ofthe carboxylate anions in the carboxylated ionic liquid, therebycreating a substituted ionic liquid. When the carboxylate ionoriginating from the acylating reagent is of a different type than thecarboxylate anions of the ionic liquid, then the substituted ionicliquid can comprise at least two different types of carboxylate anions.Thus, so long as the carboxylate anion from the carboxylated ionicliquid comprises a different acyl group than is found on the acylatingreagent, at least two different acyl groups are available foresterification of the cellulose. By way of illustration, if cellulosewas dissolved in 1-butyl-3-methylimidazolium acetate (“[BMIm]OAc” or“[BMIm]acetate”) and a propionic anhydride (“Pr₂O”) acylating reagentwere added to the carboxylated ionic liquid, the carboxylated ionicliquid can become a substituted ionic liquid, comprising a mixture of[BMIm]acetate and [BMIm]propionate. Thus, the process of forming acellulose ester via this process can be illustrated as follows:

As illustrated, contacting a solution of cellulose dissolved in[BMIm]acetate with a propionic anhydride can result in the formation ofa cellulose ester comprising both acetate ester substituents andpropionate ester substituents. Thus, at least a portion of the estergroups on the cellulose ester can originate from the ionic liquid, andat least a portion of the ester groups can originate from the acylatingreagent. Additionally, at least one of the ester groups donated by theionic liquid can be an acyl group. In one embodiment, all of the estergroups donated by the ionic liquid can be acyl groups.

Therefore, in one embodiment, the cellulose ester prepared by methods ofthe present invention can be a mixed cellulose ester. In one embodiment,the mixed cellulose ester of the present invention can comprise aplurality of first pendant acyl groups and a plurality of second acylgroups, where the first pendant acyl groups originate from the ionicliquid, and the second pendant acyl groups originate from the acylatingreagent. In one embodiment, the mixed cellulose ester can comprise amolar ratio of at least two different acyl pendant groups in the rangeof from about 1:10 to about 10:1, in the range of from about 2:8 toabout 8:2, or in the range of from 3:7 to 7:3. Additionally, the firstand second pendant acyl groups can comprise acetyl, propionyl, and/orbutyryl groups.

In one embodiment, at least one of the first pendant acyl groups can bedonated by the ionic liquid or at least one of the second pendant acylgroups can be donated by the ionic liquid. As used herein, the term“donated,” with respect to esterification, shall denote a directtransfer of an acyl group. Comparatively, the term “originated,” withrespect to esterification, can signify either a direct transfer or anindirect transfer of an acyl group. In one embodiment of the invention,at least 50 percent of the above-mentioned first pendant acyl groups canbe donated by the ionic liquid, or at least 50 percent of the secondpendant acyl groups can be donated by the ionic liquid. Furthermore, atleast 10 percent, at least 25 percent, at least 50 percent, or at least75 percent of all of the pendant acyl groups on the resulting celluloseester can result from donation of an acyl group by the ionic liquid.

In one embodiment, the above-described mixed cellulose ester can beformed by a process where a first portion of the first pendant acylgroups can initially be donated from the acylating reagent to thecarboxylated ionic liquid, and then the same acyl groups can be donatedfrom the carboxylated ionic liquid to the cellulose (i.e., indirectlytransferred from the acylating reagent to the cellulose, via the ionicliquid). Additionally, a second portion of the first pendant acyl groupscan be donated directly from the acylating reagent to the cellulose.

In a further embodiment of the present invention when 2 or moreacylating reagents are employed in the esterification of cellulose, the2 or more acylating reagents can be added as a mixture or the additioncan be staged. In a mixed addition, 2 or more acylating reagents areadded to the cellulose solution simultaneously. In the case ofcarboxylated ionic liquids, where one of the acyl groups are donated bythe ionic liquid, addition of one or more acylating reagents constitutesa mixed addition. In a staged addition, the acylating reagents are addedconsecutively. In one embodiment of the staged addition process, atleast about 80 mol percent of the first acylating reagent is allowed toreact with the cellulose prior to adding the next acylating reagent.

In one aspect of the present invention, when contacting one or moreacylating reagents with the cellulose solution reaction kinetics, theamount of acylating reagent that is added, and the order of which theyare added can also significantly influence substituent distribution orregioselectivity when the total DS is less than about 2.95.

Regioselectivity is most easily measured by determining the relativedegree of substitution (RDS) at C₆, C₃, and C₂ in the cellulose ester bycarbon 13 NMR (Macromolecules, 1991, 24, 3050-3059). In the case of oneacyl substituent or when a second acyl substituent is present in a minoramount (DS≦0.2), the RDS can be most easily determined directly byintegration of the ring carbons. When 2 or more acyl substituents arepresent in more equal amounts, in addition to determining the ring RDSit is sometimes necessary to fully substitute the cellulose ester withan additional substituent in order to independently determine the RDS ofeach substituent by integration of the carbonyl carbons. In conventionalcellulose esters, regioselectivity is generally not observed, and theRDS ratio of C₆/C₃, C₆/C₂, C₃/C₂ is generally near 1. In essence,conventional cellulose esters are random copolymers.

In the present invention, we found that when adding one or moreacylating reagents, the C₆ position of cellulose was acylated muchfaster than C₂ and C₃. Consequentially, the C₆/C₃ and C₆/C₂ RDS ratiosare greater than 1 which is characteristic of a regioselectivelysubstituted cellulose ester. The degree of regioselectivity depends uponat least one of the following factors: type of acyl substituent, contacttemperature, ionic liquid interaction, equivalents of acyl reagent,order of additions, and the like. Typically, the larger the number ofcarbon atoms in the acyl substituent, the C₆ position of the celluloseis acylated preferentially over the C₂ and C₃ position. In addition, asthe contact temperature is lowered in the esterification zone 40, the C₆position of the cellulose can be acylated preferentially over the C₂ orC₃ position. As mentioned previously, the type of ionic liquid and itsinteraction with cellulose in the process can affect theregioselectivity of the cellulose ester. For example, when carboxylatedionic liquids are utilized, a regioselectively substituted celluloseester is produced where the RDS ratio is C₆>C₃>C₂. When halide ionicliquids are utilized, a regioselectively substituted cellulose ester isproduced where the RDS ratio is C₆>C₃>C₂. This is significant in thatregioselective placement of substituents in a cellulose ester leads toregioselectively substituted cellulose esters with different physicalproperties relative to conventional cellulose esters.

In one embodiment of this invention, no protective groups are utilizedto prevent reaction of the cellulose with the acylating reagent.

In one embodiment of the present invention, the ring RDS ratio for C₆/C₃or C₆/C₂ is at least 1.05. In another embodiment, the ring RDS ratio forC₆/C₃ or C₆/C₂ is at least 1.1. Another embodiment of the presentinvention is when the ring R_(DS) ratio for C₆/C₃ or C₆/C₂ is at least1.3.

In another embodiment of the present invention, the product of the ringRDS ratio for C₆/C₃ or C₆/C₂ times the total DS [(C₆/C₃)*DS or(C₆/C₂)*DS] is at least 2.9. In another embodiment, the product of thering RDS ratio for C₆/C₃ or C₆/C₂ times the total DS is at least 3.0. Inanother embodiment, the product of the ring RDS ratio for C₆/C₃ or C₆/C₂times the total DS is at least 3.2.

In another embodiment of the present invention, the ring RDS ratio forC₆/C₃ or C₆/C₂ is at least 1.05, and the product of the ring RDS ratiofor C₆/C₃ or C₆/C₂ times the total DS is at least 2.9. In anotherembodiment, the ring RDS ratio for C₆/C₃ or C₆/C₂ is at least 1.1, andthe product of the ring RDS ratio for C₆/C₃ or C₆/C₂ times the total DSis at least 3.0. In yet another embodiment, the ring RDS ratio for C₆/C₃or C₆/C₂ is at least 1.3, and the product of the ring RDS ratio forC₆/C₃ or C₆/C₂ times the total DS is at least 3.2.

As noted previously, when 2 or more acyl substituents are present inmore equal amounts, it is sometimes desirable to integrate the carbonylcarbons in order to determine the RDS of each substituent independently.Hence, in one embodiment of the present invention, the carbonyl RDSratio of at least one acyl substituent for C₆/C₃ or C₆/C₂ is at least1.3. In another embodiment, the carbonyl RDS ratio of at least one acylsubstituent for C₆/C₃ or C₆/C₂ is at least 1.5. In another embodiment,the carbonyl RDS ratio of at least one acyl substituent for C₆/C₃ orC₆/C₂ is at least 1.7.

In another embodiment of the present invention, the product of thecarbonyl RDS ratio of at least one acyl substituent for C₆/C₃ or C₆/C₂times the DS of the acyl substituent [(C₆/C₃)*DS_(acyl) or(C₆/C₂)*DS_(acyl)] is at least 2.3. In another embodiment, the productof the carbonyl RDS ratio for C₆/C₃ or C₆/C₂ times the DS of the acylsubstituent is at least 2.5. In another embodiment, the product of thecarbonyl RDS ratio for C₆/C₃ or C₆/C₂ times the DS of the acylsubstituent is at least 2.7. In another embodiment of the presentinvention, the carbonyl RDS ratio of at least one acyl substituent forC₆/C₃ or C₆/C₂ is at least 1.3, and the product of the carbonyl RDSratio for C₆/C₃ or C₆/C₂ times the acyl DS is at least 2.3. In anotherembodiment, the carbonyl RDS ratio for C₆/C₃ or C₆/C₂ is at least 1.5,and the product of the carbonyl RDS ratio for C₆/C₃ or C₆/C₂ times theacyl DS is at least 2.5. In yet another embodiment, the carbonyl RDSratio for C₆/C₃ or C₆/C₂ is at least 1.7 the product of the carbonyl RDSratio for C₆/C₃ or C₆/C₂ times the acyl DS is at least 2.7.

Surprisingly, in one embodiment of the invention, staged additions ofthe acylating reagent gave a relative degree of substitution (RDS)different from that obtained in the mixed addition of acylating reagentMoreover, both the staged and mixed additions of the present inventionprovide a different RDS relative to other means known in the prior artfor making mixed cellulose esters which generally provide celluloseesters with a RDS at C₆, C₃, and C₂ of about 1:1:1. In some cases, theprior art methods provide a RDS where the RDS at C₆ is less than that ofC₂ and C₃.

Referring still to FIG. 1, the temperature in esterification zone 40during the above-described esterification process can be in the range offrom about 0 to about 120° C., in the range of from about 20 to about80° C., or in the range of from 25 to 50° C. Additionally, the cellulosecan have a residence time in esterification zone 40 in the range of fromabout 1 minute to about 48 hours, in the range of from about 30 minutesto about 24 hours, or in the range of from 1 to 5 hours.

Subsequent to the above-described esterification process, an esterifiedmedium can be withdrawn from esterification zone 40 via line 80. Theesterified medium withdrawn from esterification zone 40 can comprise aninitial cellulose ester. The initial cellulose ester in line 80 can be aregioselectively substituted cellulose ester. Additionally, as mentionedabove, the initial cellulose ester in line 80 can be a mixed celluloseester.

The initial cellulose ester can have a degree of substitution (“DS”) inthe range of from about 0.1 to about 3.5; about 0.1 to about 3.08, about0.1 to about 3.0, about 1.8 to about 2.9, or in the range of from 2.0 to2.6. In another embodiment, the initial cellulose ester can have a DS ofat least 2. Additionally, the initial cellulose ester can have a DS ofless than 3.0, or less than 2.9.

Furthermore, the degree of polymerization (“DP”) of the cellulose estersprepared by the methods of the present invention can be at least 10, atleast 50, at least 100, or at least 250. In another embodiment, the DPof the initial cellulose ester can be in the range of from about 5 toabout 1,000, or in the range of from 10 to 250.

The esterified medium in line 80 can comprise the initial celluloseester in an amount in the range of from about 2 to about 80 weightpercent, in the range of from about 10 to about 60 weight percent, or inthe range of from 20 to 40 weight percent based on weight of ionicliquid. In addition to the initial cellulose ester, the esterifiedmedium withdrawn from esterification zone 40 via line 80 can alsocomprise other components, such as, for example, altered ionic liquid,residual acylating reagent, and/or one or more carboxylic acids. In oneembodiment, the esterified medium in line 80 can comprise a ratio ofaltered ionic liquid to initial ionic liquid introduced into dissolutionzone 20 in an amount in the range of from about 0.01 to about 99.99weight percent, in the range of from about 10 to about 99 weightpercent, or in the range of from 90 to 98 weight percent based on thetotal amount of initial ionic liquid. Additionally, the esterifiedmedium in line 80 can comprise residual acylating reagent in an amountless than about 20 weight percent, less than about 10 weight percent, orless than 5 weight percent.

Furthermore, the esterified medium in line 80 can comprise a totalconcentration of carboxylic acids in an amount in the range of fromabout 0.01 to about 40 weight percent, in the range of from about 0.05to about 20 weight percent, or in the range of from 0.1 to 5 weightpercent. In another embodiment, the esterified medium in line 80 cancomprise a total concentration of carboxylic acids in an amount lessthan 40, less than 20, or less than 5 weight percent. Carboxylic acidsthat can be present in the esterified medium in line 80 include, but arenot limited to, formic acid, acetic acid, propionic acid, butyric acid,isobutyric acid, valeric acid, hexanoic acid, 2-ethylhexanoic acid,nonanoic acid, lauric acid, palmitic acid, stearic acid, benzoic acid,substituted benzoic acids, phthalic acid, and/or isophthalic acid.

The esterified medium in line 80 can be routed to cellulose esterrecovery/treatment zone 50. As is discussed in more detail below withreference to FIG. 2, at least a portion of the cellulose ester canoptionally be subjected to at least one randomization process inrecovery/treatment zone 50, thereby producing a randomized celluloseester. Additionally, as is discussed in more detail below with referenceto FIG. 2, at least a portion of the cellulose ester can be caused toprecipitate out of the esterified medium, at least a portion of whichcan thereafter be separated from the resulting mother liquor.

Referring still to FIG. 1, at least a portion of the cellulose esterprecipitated and recovered in recovery/treatment zone 50 can bewithdrawn via line 90 as a final cellulose ester. The final celluloseester exiting recovery/treatment zone 50 via line 90 can have a numberaverage molecular weight (“Mn”) in the range of from about 1,200 toabout 200,000, in the range of from about 6,000 to about 100,000, or inthe range of from 10,000 to 75,000. Additionally, the final celluloseester exiting recovery/treatment zone 50 via line 90 can have a weightaverage molecular weight (“Mw”) in the range of from about 2,500 toabout 420,000, in the range of from about 10,000 to about 200,000, or inthe range of from 20,000 to 150,000. Furthermore, the final celluloseester exiting recovery/treatment zone 50 via line 90 can have a Zaverage molecular weight (“Mz”) in the range of from about 4,000 toabout 850,000, in the range of from about 12,000 to about 420,000, or inthe range of from 40,000 to 330,000. The final cellulose ester exitingrecovery/treatment zone 50 via line 90 can have a polydispersity in therange of from about 1.3 to about 7, in the range of from about 1.5 toabout 5, or in the range of from 1.8 to 3. Additionally, the finalcellulose ester in line 90 can have a DP and DS as described above inrelation to the initial cellulose ester in line 80. Furthermore, thecellulose ester can be random or non-random, as is discussed in moredetail below with reference to FIG. 2. Moreover, the final celluloseester in line 90 can comprise a plurality of ester substituents asdescribed above. Also, the final cellulose ester in line 90 canoptionally be a mixed cellulose ester as described above.

In one embodiment, the cellulose ester in line 90 can be in the form ofa wet cake. The wet cake in line 90 can comprise a total liquid contentof less than 99, less than 50, or less than 25 weight percent.Furthermore, the wet cake in line 90 can comprise a total ionic liquidconcentration of less than 1, less than 0.01, or less than 0.0001 weightpercent. Additionally, the wet cake in line 90 can comprise a totalalcohol content of less than 100, less than 50, or less than 25 weightpercent. Optionally, as is discussed in greater detail below withreference to FIG. 2, the final cellulose ester can be dried to produce adry final cellulose ester product.

The cellulose esters prepared by the methods of this invention can beused in a variety of applications. Those skilled in the art willunderstand that the specific application will depend upon variouscharacteristics of the cellulose ester, such as, for example, the typeof acyl substituent, DS, molecular weight, and type of cellulose estercopolymer.

In one embodiment of the invention, the cellulose esters can be used inthermoplastic applications in which the cellulose ester is used to makefilm or molded objects. Examples of cellulose esters suitable for use inthermoplastic applications include cellulose acetate, cellulosepropionate, cellulose butyrate, cellulose acetate propionate, celluloseacetate butyrate, or mixtures thereof.

In yet another embodiment of the invention, the cellulose esters can beused in coating applications. Examples of coating applications includebut, are not limited to, automotive, wood, plastic, or metal coatingprocesses. Examples of cellulose esters suitable for use in coatingapplications include cellulose acetate, cellulose propionate, cellulosebutyrate, cellulose acetate propionate, cellulose acetate butyrate, ormixtures thereof.

In still another embodiment of the invention, the cellulose esters canbe used in personal care applications. In personal care applications,cellulose esters can be dissolved or suspended in appropriate solvents.The cellulose ester can then act as a structuring agent, delivery agent,and/or film forming agent when applied to skin or hair. Examples ofcellulose esters suitable for use in personal care applications includecellulose acetate, cellulose propionate, cellulose butyrate, celluloseacetate propionate, cellulose acetate butyrate, cellulose hexanoate,cellulose 2-ethylhexanoate, cellulose laurate, cellulose palmitate,cellulose stearate, or mixtures thereof.

In still another embodiment of the invention, the cellulose esters canbe used in drug delivery applications. In drug delivery applications,the cellulose ester can act as a film former such as in the coating oftablets or particles. The cellulose ester can also be used to formamorphous mixtures of poorly soluble drugs, thereby improving thesolubility and bioavailability of the drugs. The cellulose esters canalso be used in controlled drug delivery, where the drug can be releasedfrom the cellulose ester matrix in response to external stimuli such asa change in pH. Examples of preferred cellulose esters suitable for usein drug delivery applications include cellulose acetate, cellulosepropionate, cellulose butyrate, cellulose acetate propionate, celluloseacetate butyrate, cellulose acetate phthalate, or mixtures thereof.

In still another embodiment of the invention, the cellulose esters ofthe present invention can be used in applications involving solventcasting of film. Examples of such applications include photographicfilm, protective film, and compensation film for liquid crystallinedisplays. Examples of cellulose esters suitable for use in solvent castfilm applications include, but are not limited to, cellulose triacetate,cellulose acetate, cellulose propionate, and cellulose acetatepropionate.

In an embodiment of the invention, films are produced comprisingcellulose esters of the present invention and are used as protective andcompensation films for liquid crystalline displays (LCD). These filmscan be prepared by solvent casting as described in US application2009/0096962 or by melt extrusion as described in US application2009/0050842, both of which are incorporated in their entirety in thisinvention to the extent they do not contradict the statements herein.

When used as a protective film, the film is typically laminated toeither side of an oriented, iodinated polyvinyl alcohol (PVOH)polarizing film to protect the PVOH layer from scratching and moisture,while also increasing structural rigidity. When used as compensationfilms (or plates), they can be laminated with the polarizer stack orotherwise included between the polarizer and liquid crystal layers.These compensation films can improve the contrast ratio, wide viewingangle, and color shift performance of the LCD. The reason for thisimportant function is that for a typical set of crossed polarizers usedin an LCD, there is significant light leakage along the diagonals(leading to poor contrast ratio), particularly as the viewing angle isincreased. It is known that various combinations of optical films can beused to correct or “compensate” for this light leakage. Thesecompensation films must have certain well-defined retardation (orbirefringence) values, which vary depending on the type of liquidcrystal cell or mode used because the liquid crystal cell itself willalso impart a certain degree of undesirable optical retardation thatmust be corrected.

Compensation films are commonly quantified in terms of birefringence,which is, in turn, related to the refractive index n. For celluloseesters, the refractive index is approximately 1.46 to 1.50. For anunoriented isotropic material, the refractive index will be the sameregardless of the polarization state of the entering light wave. As thematerial becomes oriented, or otherwise anisotropic, the refractiveindex becomes dependent on material direction. For purposes of thepresent invention, there are three refractive indices of importancedenoted n_(x), n_(y), and n_(z), which correspond to the machinedirection (MD), the transverse direction (TD), and the thicknessdirection, respectively. As the material becomes more anisotropic (e.g.by stretching), the difference between any two refractive indices willincrease. This difference in refractive index is referred to as thebirefringence of the material for that particular combination ofrefractive indices. Because there are many combinations of materialdirections to choose from, there are correspondingly different values ofbirefringence. The two most common birefringence parameters are theplanar birefringence defined as Δ_(e)=n_(x)−n_(y), and the thicknessbirefringence (Δ_(th)) defined as: Δ_(th)=n_(z)−(n_(x)+n_(y))/2. Thebirefringence Δ_(e) is a measure of the relative in-plane orientationbetween the MD and TD and is dimensionless. In contrast, Δ_(th) gives ameasure of the orientation of the thickness direction, relative to theaverage planar orientation.

Optical retardation (R) is related the birefringence by the thickness(d) of the film: R_(e)=Δ_(e)d=(n_(x)−n_(y))d;R_(th)=Δ_(th)d=[n_(z)−(n_(x)+n_(y))/2]. Retardation is a direct measureof the relative phase shift between the two orthogonal optical waves andis typically reported in units of nanometers (nm). Note that thedefinition of R_(th) varies with some authors, particularly with regardsto the sign (±).

Compensation films or plates can take many forms depending upon the modein which the LCD display device operates. For example, a C-platecompensation film is isotropic in the x-y plane, and the plate can bepositive (+C) or negative (−C). In the case of +C plates,n_(x)=n_(y)<n_(z). In the case of −C plates, n_(x)=n_(y)>n_(z). Anotherexample is A-plate compensation film which is isotropic in the y-zdirection, and again, the plate can be positive (+A) or negative (−A).In the case of +A plates, n_(x)>n_(y)=n_(z). In the case of −A plates,n_(x)<n_(y)=n_(z).

In general, aliphatic cellulose esters provide values of R_(th) rangingfrom about 0 to about −350 nm at a film thickness of 60 μm. The mostimportant factors that influence the observed R_(th) is type ofsubstituent and the degree of substitution of hydroxyl (DS_(OH)). Filmproduced using cellulose mixed esters with very low DS_(OH) in Shelby etal. (US 2009/0050842) had R_(th) values ranging from about 0 to about−50 nm. By significantly increasing DS_(OH) of the cellulose mixedester, Shelton et al. (US 2009/0096962) demonstrated that largerabsolute values of R_(th) ranging from about −100 to about −350 nm couldbe obtained. Cellulose acetates typically provide R_(th) values rangingfrom about −40 to about −90 nm depending upon DS_(OH).

One aspect of the present invention relates to compensation filmcomprising regioselectively substituted cellulose esters wherein thecompensation film has an R_(th) range from about −400 to about +100 nm.In another embodiment of the invention, compensation films are providedcomprising regioselectively substituted cellulose esters having a totalDS from about 1.5 to about 2.95 of a single acyl substituent (DS≧0.2 ofa second acyl substituent) and wherein the compensation film has anR_(th) value from about −400 to about +100 nm.

In one embodiment of the invention, the regioselectively substitutedcellulose esters utilized for producing films are selected from thegroup consisting of cellulose acetate, cellulose propionate, andcellulose butyrate wherein the regioselectively substituted celluloseester has a total DS from about 1.6 to about 2.9. In another embodimentof the invention, the compensation film has R_(th) values from about−380 to about −110 nm and is comprised of a regioselectively substitutedcellulose propionate having a total DS of about 1.7 to about 2.5. In yetanother embodiment, the compensation film has R_(th) values from about−380 to about −110 nm and is comprised of a regioselectively substitutedcellulose propionate having a total DS of about 1.7 to about 2.5 and aring RDS ratio for C₆/C₃ or C₆/C₂ of at least 1.05. In anotherembodiment, the compensation film has R_(th) values from about −60 toabout +100 nm and is comprised of regioselectively substituted cellulosepropionate having a total DS of about 2.6 to about 2.9. In yet anotherembodiment, the compensation film has R_(th) values from about −60 toabout +100 nm and is comprised of regioselectively substituted cellulosepropionate having a total DS of about 2.6 to about 2.9 and a ring RDSratio for C₆/C₃ or C₆/C₂ of at least 1.05. In another embodiment, thecompensation film has R_(th) values from about 0 to about +100 nm and iscomprised of a regioselectively substituted cellulose propionate havinga total DS of about 2.75 to about 2.9. In yet another embodiment, thecompensation film has R_(th) values from about 0 to about +100 nm and iscomprised of a regioselectively substituted cellulose propionate havinga total DS of about 2.75 to about 2.9 and a ring RDS ratio for C₆/C₃ orC₆/C₂ of at least 1.05.

Another aspect of the present invention relates to compensation filmwith an R_(th) range from about −160 to about +270 nm comprised ofregioselectively substituted cellulose esters having a total DS fromabout 1.5 to about 3.0 of a plurality of 2 or more acyl substituents. Inone embodiment of this invention, the cellulose esters can be selectedfrom the group consisting of cellulose acetate propionate, celluloseacetate butyrate, cellulose benzoate propionate, and cellulose benzoatebutyrate; wherein the regioselectively substituted cellulose ester has atotal DS from about 2.0 to about 3.0. In another embodiment, thecompensation film has R_(th) values from about −160 to about 0 nm and iscomprised of a regioselectively substituted cellulose acetate propionatehaving a total DS of about 2.0 to about 3.0, a ring RDS ratio for C₆/C₃or C₆/C₂ of at least 1.05, and a carbonyl RDS ratio for at least oneacyl substituent for C₆/C₃ or C₆/C₂ of at least about 1.3. In anotherembodiment, the compensation film has R_(th) values from about +100 toabout +270 nm and is comprised of a regioselectively substitutedcellulose benzoate propionate having a total DS of about 2.0 to about3.0, a ring RDS ratio for C₆/C₃ or C₆/C₂ of at least 1.05, and acarbonyl RDS ratio for at least one acyl substituent for C₆/C₃ or C₆/C₂of at least about 1.3. In another embodiment, the compensation film hasR_(th) values from about +100 to about +270 nm and is comprised of aregioselectively substituted cellulose benzoate propionate having atotal DS of about 2.0 to about 3.0, a ring RDS ratio for C₆/C₃ or C₆/C₂of at least 1.05, a carbonyl RDS ratio for at least one acyl substituentfor C₆/C₃ or C₆/C₂ of at least about 1.3, and the benzoate substituentis located primarily at C2 or C3.

Referring still to FIG. 1, at least a portion of the mother liquorproduced in cellulose ester recovery/treatment zone 50 can be withdrawnvia line 86 and routed to ionic liquid recovery/treatment zone 60. Aswill be discussed in further detail below with reference to FIG. 2, themother liquor can undergo various treatments in ionic liquidrecovery/treatment zone 60. Such treatment can include, but is notlimited to, volatiles removal and reformation of the ionic liquid.Reformation of the ionic liquid can include, but is not limited to, (1)anion homogenization, and (2) anion exchange. Accordingly, a recycledionic liquid can be formed in ionic liquid recovery/treatment zone 60.

In one embodiment, at least a portion of the recycled ionic liquid canbe withdrawn from ionic liquid recovery/treatment zone 60 via line 70.The recycled ionic liquid in line 70 can have a composition such asdescribed above in relation to the ionic liquid in line 64 of FIG. 1.The production and composition of the recycled ionic liquid will bediscussed in greater detail below with reference to FIG. 2. As mentionedabove, at least a portion of the recycled ionic liquid in line 70 can berouted back to dissolution zone 20. In one embodiment, at least about 80weight percent, at least about 90 weight percent, or at least 95 weightpercent of the recycled ionic liquid produced in ionic liquidrecovery/treatment zone 60 can be routed to dissolution zone 20.

Referring now to FIG. 2, a more detailed diagram for the production ofcellulose esters is depicted, including optional steps for improving theoverall efficacy and/or efficiency of the esterification process. In theembodiment depicted in FIG. 2, a cellulose can be introduced into anoptional modification zone 110 via line 162. The cellulose fed tooptional modification zone 110 can be substantially the same as thecellulose in line 62 described above with reference to FIG. 1. Inoptional modification zone 110, the cellulose can be modified employingat least one modifying agent.

As mentioned above, water may be employed as the modifying agent. Thus,in one embodiment of the present invention, a water-wet cellulose can bewithdrawn from optional modification zone 110 and added to one or moreionic liquids in dissolution zone 120. In one embodiment, the cellulosecan be mixed with water then pumped into one or more ionic liquids as aslurry. Alternatively, excess water can be removed from the cellulose,and thereafter the cellulose can be added to the one or more ionicliquids in the form of a wet cake. In this embodiment, the cellulose wetcake can contain associated water in an amount in the range of fromabout 10 to about 95 weight percent, in the range of from about 20 toabout 80 weight percent, or in the range of from 25 to 75 weightpercent, based on the combined weight of the cellulose and associatedwater.

Though not wishing to be bound by theory, the addition of water wetcellulose has unexpectedly and unpredictably been found to provide atleast three heretofore unknown benefits. First, water can increasedispersion of the cellulose in the one or more ionic liquids so thatwhen removal of water is initiated while heating the cellulose, thecellulose rapidly dissolves in the one or more ionic liquids. Secondly,water appears to reduce the melting points of ionic liquids that arenormally solids at room temperature, thus allowing processing of ionicliquids at ambient temperatures. A third benefit is that the molecularweight of cellulose esters prepared using initially water wet celluloseis reduced during the above-discussed esterification in esterificationzone 40 when compared to cellulose esters prepared using initially drycellulose.

This third benefit is particularly surprising and useful. Under typicalcellulose ester processing conditions, the molecular weight of celluloseis not reduced during dissolution or during esterification. That is, themolecular weight of the cellulose ester product is directlyproportionate to the molecular weight of the initial cellulose. Typicalwood pulps used to prepare cellulose esters generally have a DP in therange of from about 1,000 to about 3,000. However, the desired DP rangeof cellulose esters can be from about 10 to about 500. Thus, in theabsence of molecular weight reduction during esterification, thecellulose must be specially treated prior to dissolving the cellulose inthe ionic liquid or after dissolving in the ionic liquid but prior toesterification. However, when employing water as at least one of theoptional modifying agents, pretreatment of the cellulose is not requiredsince molecular weight reduction can occur during esterification.Accordingly, in one embodiment of the present invention, the DP of themodified cellulose subjected to esterification can be within about 10percent of, within about 5 percent of, within 2 percent of, orsubstantially the same as the DP of the initial cellulose subjected tomodification. However, the DP of the cellulose ester produced inaccordance with embodiments of the present invention can be less thanabout 90 percent, less than about 70 percent, or less than 50 percent ofthe DP of the modified cellulose subjected to esterification.

Referring still to FIG. 2, the optionally modified cellulose in line 166can be introduced into dissolution zone 120. Once in dissolution zone120, the optionally modified cellulose can be dispersed in one or moreionic liquids, as described above with reference to dissolution zone 20in FIG. 1. Subsequently, at least a portion of the modifying agent inthe resulting cellulose/ionic liquid mixture can be removed. In oneembodiment, at least 50 weight percent of all modifying agents can beremoved, at least 75 weight percent of all modifying agents can beremoved, at least 95 weight percent of all modifying agents can beremoved, or at least 99 weight percent of all modifying agents can beremoved from the cellulose/ionic liquid mixture. Removal of one or moremodifying agents in dissolution zone 120 can be accomplished by anymeans known in the art for liquid/liquid separation, such as, forexample, distillation, flash vaporization, and the like. Removedmodifying agent can be withdrawn from dissolution zone 120 via line 124.

After removal of the modifying agent, dissolution zone 120 can produce acellulose solution in substantially the same manner as dissolution zone20, as described above with reference to FIG. 1. Thereafter, a cellulosesolution can be withdrawn from dissolution zone 120 via line 176. Thecellulose solution in line 176 can comprise ionic liquid, cellulose, anda residual concentration of one or more optional modifying agents. Thecellulose solution in line 176 can comprise cellulose in an amount inthe range of from about 1 to about 40 weight percent, in the range offrom about 5 to about 30 weight percent, or in the range of from 10 to20 weight percent, based on the weight of the ionic liquid. Furthermore,the cellulose solution in line 176 can comprise a cumulative amount ofresidual modifying agents in an amount of less than about 50 weightpercent, less than about 25 weight percent, less than about 15 weightpercent, less than about 5 weight percent, or less than 1 weightpercent.

In the embodiment of FIG. 2, at least a portion of the cellulosesolution in line 176 can be introduced into esterification zone 140.Esterification zone 140 can be operated in substantially the same manneras esterification zone 40, as described above with reference to FIG. 1.For example, an acylating reagent can be introduced into esterificationzone 140 via line 178. As in esterification zone 40, the acylatingreagent can esterify at least a portion of the cellulose inesterification zone 140. Additionally, as described above, at least aportion of the resulting cellulose ester can comprise one or more estersubstituents that originated from and or were donated by the ionicliquid.

After esterification in esterification zone 140, an esterified mediumcan be withdrawn via line 180. The esterified medium in line 180 can besubstantially the same as the esterified medium in line 80, as describedabove with reference to FIG. 1. Thus, the esterified medium in line 180can comprise an initial cellulose ester and other components, such as,for example, altered ionic liquid, residual acylating reagent, one ormore carboxylic acids, and/or one or more catalysts. The concentrationsof the initial cellulose ester and other components in the esterifiedmedium in line 180 can be substantially the same as the esterifiedmedium in line 80 described above with reference to FIG. 1.

Referring still to FIG. 2, as mentioned above, the initial celluloseester produced in esterification zone 140 can be a non-random celluloseester. In one embodiment, at least a portion of the initial cellulose inline 180 can optionally be introduced into randomization zone 151 toundergo randomization, thereby creating a random cellulose ester.Randomization of the initial cellulose can comprise introducing at leastone randomizing agent into randomization zone 151 via line 181.Additionally, as will be discussed in further detail below, at least aportion of the randomization agent introduced into randomization zone151 can be introduced via line 194.

The randomization agent employed in the present invention can be anysubstance capable lowering the DS of the cellulose ester via hydrolysisor alcoholysis, and/or by causing migration of at least a portion of theacyl groups on the cellulose ester from one hydroxyl to a differenthydroxyl, thereby altering the initial monomer distribution. Examples ofsuitable randomizing agents include, but are not limited to water and/oralcohols. Alcohols suitable for use as the randomizing agent include,but are not limited to methanol, ethanol, n-propanol, i-propanol,n-butanol, i-butanol, t-butanol, phenol and the like. In one embodiment,methanol can be employed as the randomizing agent introduced via line181.

The amount of randomizing agent introduced into randomization zone 151can be in the range of from about 0.5 to about 20 weight percent, or inthe range of from 3 to 10 weight percent, based on the total weight ofthe resulting randomization medium in randomization zone 151. Therandomization medium can have any residence time in randomization zone151 suitable to achieve the desired level of randomization. In oneembodiment, the randomization medium can have a residence time inrandomization zone 151 in the range of from about 1 min. to about 48hours, in the range of from about 30 min. to about 24 hours, or in therange of from 2 to 12 hours. Additionally, the temperature inrandomization zone 151 during randomization can be any temperaturesuitable to achieve the desired level of randomization. In oneembodiment, the temperature in randomization zone 151 duringrandomization can be in the range of from about 20 to about 120° C., inthe range of from about 30 to about 100° C., or in the range of from 50to 80° C.

Those skilled in the art will understand that the DS and DP of thecellulose ester random copolymer might be less than that of thecellulose ester non-random copolymer. Accordingly, in this embodimentthe non-random cellulose ester entering randomization zone 151 mayoptionally have a greater DS and/or DP than the target DS and/or DP ofthe randomized cellulose ester.

In one embodiment of the present invention, it may be desirable toproduce cellulose esters that are at least partially soluble in acetone.Accordingly, the initial cellulose ester produced in esterification zone140 can bypass optional randomization zone 151, thereby producing afinal non-random cellulose ester. Non-random cellulose esters preparedby the methods of the present invention can be at least partiallysoluble in acetone when they have a DS in the range of from about 2.1 toabout 2.4, in the range of from about 2.28 to about 2.39 or in the rangeof from 2.32 to 2.37.

After optional randomization, an optionally randomized medium can bewithdrawn from randomization zone 151 via line 182. The optionallyrandomized medium can comprise randomized cellulose ester and residualrandomizing agent. In one embodiment, the optionally randomized mediumin line 182 can comprise randomized cellulose ester in an amount in therange of from about 2 to about 80 weight percent, in the range of fromabout 10 to about 60 weight percent, or in the range of from 20 to 40weight percent based on the weight of the ionic liquid. Additionally,the optionally randomized medium can comprise residual randomizing agentin the range of from about 0.5 to about 20 weight percent, or in therange of from 3 to 10 weight percent, based on the total weight of theresulting randomized medium.

Additionally, the optionally randomized medium in line 182 can compriseother components, such as those described above with reference to theesterified medium in line 180 and with reference to the esterifiedmedium in line 80 of FIG. 1. Such components include, but are notlimited to, altered ionic liquid, residual acylating reagent, one ormore carboxylic acids, and/or one or more catalysts.

Following optional randomization, at least a portion of the esterifiedand optionally randomized medium in line 182 can be introduced intoprecipitation zone 152. Precipitation zone 152 can operate to cause atleast a portion of the cellulose ester from the esterified andoptionally randomized medium to precipitate. Any methods known in theart suitable for precipitating a cellulose ester can be employed inprecipitation zone 152. In one embodiment, a precipitating agent can beintroduced into precipitation zone 152, thereby causing at least aportion of the cellulose ester to precipitate. In one embodiment, theprecipitating agent can be a non-solvent for the cellulose ester.Examples of suitable non-solvents that can be employed as theprecipitating agent include, but are not limited to, C₁ to C₈ alcohols,water, or a mixture thereof. In one embodiment, the precipitating agentintroduced into precipitation zone 152 can comprise methanol.

The amount of precipitating agent introduced into precipitation zone 152can be any amount sufficient to cause at least a portion of thecellulose ester to precipitate. In one embodiment, the amount ofprecipitating agent introduced into precipitation zone 152 can be atleast about 20 volumes, at least 10 volumes, or at least 4 volumes,based on the total volume of the medium entering precipitation zone 152.The resulting precipitation medium can have any residence time inprecipitation zone 152 suitable to achieve the desired level ofprecipitation. In one embodiment, the precipitation medium can have aresidence time in precipitation zone 152 in the range of from about 1 toabout 300 min., in the range of from about 10 to about 200 min., or inthe range of from 20 to 100 min. Additionally, the temperature inprecipitation zone 152 during precipitation can be any temperaturesuitable to achieve the desired level of precipitation. In oneembodiment, the temperature in precipitation zone 152 duringprecipitation can be in the range of from about 0 to about 120° C., inthe range of from about 20 to about 100° C., or in the range of from 25to 50° C. The amount of cellulose ester precipitated in precipitationzone 152 can be at least 50 weight percent, at least 75 weight percent,or at least 95 weight percent, based on the total amount of celluloseester in precipitation zone 152.

After precipitation in precipitation zone 152, a cellulose ester slurrycan be withdrawn via line 184 comprising a final cellulose ester. Thecellulose ester slurry in line 184 can have a solids content of lessthan about 50 weight percent, less than about 25 weight percent, or lessthan 1 weight percent.

At least a portion of the cellulose ester slurry in line 184 can beintroduced into separation zone 153. In separation zone 153, at least aportion of the liquid content of the cellulose ester slurry can beseparated from the solids portion. Any solid/liquid separation techniqueknown in the art for separating at least a portion of a liquid from aslurry can be used in separation zone 153. Examples of suitablesolid/liquid separation techniques suitable for use in the presentinvention include, but are not limited to, centrifugation, filtration,and the like. In one embodiment, at least 50 weight percent, at least 70weight percent, or at least 90 weight percent of the liquid portion ofthe cellulose ester slurry can be removed in separation zone 153.

Furthermore, separation zone 153 can have any temperature or pressuresuitable for solid liquid separation. In one embodiment, the temperaturein separation zone 153 during separation can be in the range of fromabout 0 to about 120° C., in the range of from about 20 to about 100°C., or in the range of from 25 to 50° C.

After separation in separation zone 153, a cellulose ester wet cake canbe withdrawn from separation zone 153 via line 187. The cellulose esterwet cake in line 187 can have a total solids content of at least 1weight percent, at least 50 weight percent, or at least 75 weightpercent. Additionally, the cellulose ester wet cake in line 187 cancomprise cellulose ester in an amount of at least 70 weight percent, atleast 80 weight percent, or at least 90 weight percent. Additionally, aswill be discussed in greater detail below, at least a portion of theseparated liquids from separation zone 153 can be withdrawn via line186.

Once removed from separation zone 153, at least a portion of thecellulose ester solids from the cellulose ester wet cake can be washedin wash zone 154. Any method known in the art suitable for washing a wetcake can be employed in wash zone 154. An example of a washing techniquesuitable for use in the present invention includes, but is not limitedto, a multi-stage counter-current wash. In one embodiment, a wash liquidthat is a non-solvent for cellulose ester can be introduced into washzone 154 via line 188 to wash at least a portion of the cellulose estersolids. Such wash liquids include, but are not limited to, a C₁ to C₈alcohol, water, or a mixture thereof. In one embodiment, the wash liquidcan comprise methanol. Additionally, as will be described in greaterdetail below, at least a portion of the wash liquid can be introducedinto wash zone 154 via line 194.

In one embodiment, washing of the cellulose ester solids in wash zone153 can be performed in such a manner that at least a portion of anyundesired by-products and/or color bodies are removed from the celluloseester solids and/or ionic liquid. In one embodiment, the non-solventwash liquid can contain a bleaching agent in the range of from about0.001 to about 50 weight percent, or in the range of from 0.01 to 5weight percent based on the total weight of the wash fluid. Examples ofbleaching agents suitable for use in the present invention include, butare not limited to, chlorites, such as sodium chlorite (NaClO₂);hypohalites, such as NaOCl, NaOBr and the like; peroxides, such ashydrogen peroxide and the like; peracids, such as peracetic acid and thelike; metals, such as Fe, Mn, Cu, Cr and the like; sodium sulfites, suchas sodium sulfite (Na₂SO₃), sodium metabisulfite (Na₂S₂O₅), sodiumbisulfite (NaHSO₃) and the like; perborates, such as sodium perborate(NaBO₃.nH₂O where n=1 or 4); chlorine dioxide (ClO₂); oxygen; and ozone.In one embodiment, the bleaching agent employed in the present inventioncan include hydrogen peroxide, NaOCl, sodium chlorite and/or sodiumsulfite. Washing in wash zone 153 can be sufficient to remove at least50, at least 70, or at least 90 percent of the total amount ofbyproducts and/or color bodies.

After washing in wash zone 154, a washed cellulose ester product can bewithdrawn via line 189. The washed cellulose ester product in line 189can be in the form of a wet cake, and can comprise solids in an amountof at least 1, at least 50, or at least 75 weight percent. Additionally,the washed cellulose ester product in line 189 can comprise celluloseester in an amount of at least 1, at least 50, or at least 75 weightpercent.

The washed cellulose ester product can optionally be dried in dryingzone 155. Drying zone 155 can employ any drying methods known in the artto remove at least a portion of the liquid content of the washedcellulose ester product. Examples of drying equipment suitable for usein drying zone 155 include, but are not limited to, rotary dryers,screw-type dryers, paddle dryers, and/or jacketed dryers. In oneembodiment, drying in drying zone 155 can be sufficient to produce adried cellulose ester product comprising less than 5, less than 3, orless than 1 weight percent liquids.

After drying in drying zone 155, a final cellulose ester product can bewithdrawn via line 190. The final cellulose ester product in line 190can be substantially the same as the final cellulose ester product inline 90, as described above with reference to FIG. 1.

Referring still to FIG. 2, as mentioned above at least a portion of theseparated liquids generated in separation zone 153 can be withdrawn vialine 186 as a recycle stream. The recycle stream in line 186 cancomprise altered ionic liquid, one or more carboxylic acids, residualmodifying agent, residual catalyst, residual acylating reagent, residualrandomizing agent, and/or residual precipitation agent. As used herein,the term “altered ionic liquid” refers to an ionic liquid that haspreviously passed through a cellulose esterification step wherein atleast a portion of the ionic liquid acted as acyl group donor and/orrecipient. As used herein, the term “modified ionic liquid” refers to anionic liquid that has previously been contacted with another compound inan upstream process step. Therefore, altered ionic liquids are a subsetof modified ionic liquids, where the upstream process step is celluloseesterification.

In one embodiment, the recycle stream in line 186 can comprise alteredionic liquid, one or more carboxylic acids, one or more alcohols, and/orwater. In one embodiment, the recycle stream in line 186 can comprisealtered ionic liquid in an amount in the range of from about 10 to about99.99 weight percent, in the range of from about 50 to about 99 weightpercent, or in the range of from 90 to 98 weight percent, based on thetotal weight of the recycle stream in line 186. In one embodiment, thealtered ionic liquid can comprise an ionic liquid having at least twodifferent anions: primary anions and secondary anions. At least aportion of the primary anions in the altered ionic liquid originate fromthe initial ionic liquid introduced into dissolution zone 120 via line164, as described above. Additionally, at least a portion of thesecondary anions in the altered ionic liquid originate from theacylating reagent introduced into esterification zone 140, as describedabove. In one embodiment, the altered ionic liquid can comprise primaryanions and secondary anions in a ratio in the range of from about 100:1to about 1:100, in the range of from about 1:10 to about 10:1, or in therange of from 1:2 to about 2:1. Additionally, the altered ionic liquidcan comprise a plurality of cations, such as those described above withreference to the initial ionic liquid in line 68 of FIG. 1.

The recycle stream in line 186 can comprise a total amount of carboxylicacids in an amount in the range of from about 5 to about 60 weightpercent, in the range of from about 10 to about 40 weight percent, or inthe range of from 15 to 30 weight percent based on the total weight ofionic liquid in the recycle stream in line 186. Examples of suitablecarboxylic acids the recycle stream in line 186 can comprise include,but are not limited to, acetic acid, propionic acid, butyric acid,isobutyric acid, valeric acid, hexanoic acid, 2-ethylhexanoic acid,nonanoic acid, lauric acid, palmitic acid, stearic acid, benzoic acid,substituted benzoic acids, phthalic acid, and isophthalic acid. In oneembodiment, at least 50 weight percent, at least 70 weight percent, orat least 90 weight percent of the carboxylic acids in the recycle streamin line 186 are acetic, propionic, and/or butyric acids.

Furthermore, the recycle stream in line 186 can comprise a totalconcentration of alcohols in an amount of at least 20 volumes, at least10 volumes, or at least 4 volumes, based on the total volume of therecycle stream. Examples of suitable alcohols the recycle stream in line186 can comprise include, but are not limited to, C₁ to C₈ straight- orbranched-chain alcohols. In one embodiment, at least 50 weight percent,at least 70 weight percent, or at least 90 weight percent of the alcoholin the separated ionic liquids in line 186 comprises methanol. Moreover,the recycle stream in line 186 can comprise water in an amount of atleast 20 volumes, at least 10 volumes, or at least 4 volumes, based onthe total volume of the recycle stream.

As depicted in FIG. 2, at least a portion of the recycle stream in line186 can be introduced into ionic liquid recovery/treatment zone 160.Ionic liquid recovery/treatment zone 160 can operate to segregate and/orreform at least a portion of the recycle stream from line 186. In oneembodiment, at least a portion of the recycle stream can undergo atleast one flash vaporization and/or distillation process to remove atleast a portion of the volatile components in the recycle stream. Atleast 40 weight percent, at least 75 weight percent, or at least 95weight percent of the volatile components in the recycle stream can beremoved via flash vaporization. The volatile components removed from therecycle stream can comprise one or more alcohols. In one embodiment, thevolatile components can comprise methanol. After vaporization, theresulting volatiles-depleted recycle stream can comprise a total amountof alcohols in the range of from about 0.1 to about 60 weight percent,in the range of from about 5 to about 55 weight percent, or in the rangeof from 15 to 50 weight percent.

In one embodiment, at least a portion of the carboxylic acids can beremoved from the recycle stream. This can be accomplished by firstconverting at least a portion of the carboxylic acids to carboxylateesters. In this embodiment, at least a portion of the recycle stream canbe placed into a pressurized reactor where the recycle stream can betreated at a temperature, pressure, and time sufficient to convert theat least a portion of the carboxylic acid to methyl esters, by reactingthe carboxylic acids with the alcohol present in the recycle stream.During the esterification, the pressurized reactor can have atemperature in the range of from 100 to 180° C., or in the range of from130 to 160° C. Additionally, the pressure in the pressurized reactorduring esterification can be in the range of from about 10 to about1,000 pounds per square inch gauge (“psig”), or in the range of from 100to 300 psig. The recycle stream can have a residence time in thepressurized reactor in the range of from about 10 to about 1,000minutes, or in the range of from 120 to 600 minutes. Prior to theabove-described esterification, the alcohol and carboxylic acid can bepresent in the recycle stream in a molar ratio in the range of fromabout 1:1 to about 30:1, in the range of from about 3:1 to about 20:1,or in the range of from 5:1 to 10:1 alcohol-to-carboxylic acid. In oneembodiment, at least 5, at least 20, or at least 50 mole percent of thecarboxylic acids can be esterified during the above-describedesterification.

As mentioned above, at least a portion of the carboxylic acids can beacetic, propionic, and/or butyric acids. Additionally, as mentionedabove, the alcohol present in the recycle stream can be methanol.Accordingly, the above-described esterification process can operate toproduce methyl acetate, methyl propionate, and/or methyl butyrate.Subsequent to esterification, at least 10, at least 50, or at least 95weight percent of the resulting carboxylate esters can be removed fromthe recycle stream by any methods known in the art. As depicted in FIG.2, at least a portion of the carboxylate esters produced by the abovedescribed esterification can be routed to esterification zone 140 vialine 196. Carboxylate esters introduced into esterification zone 140 canbe employed as immiscible cosolvents, as described above. In anotherembodiment, at least a portion of the carboxylate esters can beconverted to anhydrides by CO insertion.

In another embodiment of the present invention, at least a portion ofthe altered ionic liquid present in the recycle stream can undergoreformation. Reformation of the altered ionic liquid can optionally beperformed simultaneously with the esterification of the carboxylic acidsin the recycle stream. Alternatively, reformation of the altered ionicliquid can be performed subsequently to the esterification of thecarboxylic acids in the recycle stream. Reformation of the altered ionicliquid can comprise at least one anion exchange process.

In one embodiment, reformation of the altered ionic liquid can compriseanion homogenization via anion exchange, such that substantially all ofthe anions of the altered ionic liquid are converted to the same type ofanion. In this embodiment, at least a portion of the altered ionicliquid can be contacted with at least one alkyl formate. Alkyl formatessuitable for use in the present invention include, but are not limitedto, methyl formate, ethyl formate, propyl formate, isopropyl formate,butyl formate, isobutyl formate, tert-butyl formate, hexyl formate,octyl formate, and the like. In one embodiment, the alkyl formate cancomprise methyl formate. Additionally, reformation of the altered ionicliquid can be performed in the presence of one or more alcohols.Alcohols suitable for use in this embodiment of the invention include,but are not limited to, alkyl or aryl alcohols such as methanol,ethanol, n-propanol, i-propanol, n-butanol, i-butanol, t-butanol, phenoland the like. In one embodiment, the alcohol present during reformationcan comprise methanol.

The temperature during reformation of the altered ionic liquid can be inthe range of from about 100 to about 200° C., or in the range of from130 to about 170° C. Additionally, the pressure during reformation ofthe altered ionic liquid can be at least 700 kPa, or at least 1,025 kPa.Furthermore, the reaction time of the reformation of the altered ionicliquid can be in the range of from about 10 min. to about 24 hours, orin the range of from 3 to 18 hours.

As mentioned above, reformation of the altered ionic liquid can compriseanion homogenization. In one embodiment, the resulting reformed ionicliquid can have an at least 90, at least 95, or at least 99 percentuniform anion content. Additionally, the reformed ionic liquid cancomprise an alkyl amine formate. In one embodiment, the amine of thealkyl amine formate can be an imidazolium. Examples of alkyl amineformates suitable for use as the reformed ionic liquid include, but arenot limited to, 1-methyl-3-methylimidazolium formate,1-ethyl-3-methylimidazolium formate, 1-propyl-3-methylimidazoliumformate, 1-butyl-3-methylimidazolium formate,1-hexyl-3-methylimidazolium formate, and/or 1-octyl-3-methylimidazoliumformate.

Following reformation, at least a portion of the volatile components ofthe reformed ionic liquid can optionally be removed via any methodsknown in the art for removing volatile components. Volatile componentsremoved from the reformed ionic liquid can include, for example,carboxylate esters, such as those formed via the above describedcarboxylic acid esterification process. Thereafter, at least a portionof the reformed ionic liquid can undergo at least one anion exchangeprocess to replace at least a portion of the anions of the reformedionic liquid thereby forming a carboxylated ionic liquid. In oneembodiment, the reformed ionic liquid can be contacted with at least onecarboxylate anion donor to at least partially effect the anion exchange.Carboxylate anion donors suitable for use in this embodiment include,but are not limited to, one or more carboxylic acids, anhydrides, oralkyl carboxylates. Additionally, the carboxylate anion donors cancomprise one or more C₂ to C₂₀ straight- or branched-chain alkyl or arylcarboxylic acids, anhydrides, or methyl esters. Furthermore, thecarboxylate anion donor can be one or more C₂ to C₁₂ straight-chainalkyl carboxylic acids, anhydrides, or methyl esters. Moreover, thecarboxylate anion donor can be one or more C₂ to C₄ straight-chain alkylcarboxylic acids, anhydrides, or methyl esters. The resultingcarboxylated ionic liquid can be substantially the same as thecarboxylated ionic liquid described above with reference to thecarboxylated ionic liquid in line 64 of FIG. 1.

When contacting the reformed ionic liquid with one or more carboxylateanion donors, the contacting can be carried out in a contact mixturefurther comprising alcohol or water. In one embodiment, the alcohol orwater can be present in the contact mixture in the range of from 0.01 to20 molar equivalents per alkyl amine formate, or in the range of from 1to 10 molar equivalents per alkyl amine formate. In one embodiment,methanol can be present in the contact mixture in the range of from 1 to10 molar equivalents per alkyl amine formate.

Referring still to FIG. 2, in one embodiment at least a portion of thecarboxylated ionic liquid produced in ionic liquid recovery/treatmentzone 160 can be in a treated ionic liquid mixture further comprising atleast one alcohol, at least one residual carboxylic acid, and/or water.The one or more alcohols and/or residual carboxylic acids can besubstantially the same as described above with reference to the recyclestream in line 186. The treated ionic liquid mixture can be subjected toat least one liquid/liquid separation process to remove at least aportion of the one or more alcohols. Such separation process cancomprise any liquid/liquid separation process known in the art, such as,for example, flash vaporization and/or distillation. Additionally, thetreated ionic liquid mixture can be subjected to at least oneliquid/liquid separation process to remove at least a portion of thewater. Such separation process can comprise any liquid/liquid separationprocess known in the art, such as, for example, flash vaporizationand/or distillation.

In one embodiment, at least 50, at least 70, or at least 85 weightpercent of the alcohols and/or water can be removed from the treatedionic liquid mixture thereby producing a recycled carboxylated ionicliquid. At least a portion of the alcohol separated from the treatedionic liquid mixture can optionally be removed from ionic liquidrecovery/treatment zone 160 via line 194. The one or more alcohols inline 194 can thereafter optionally be routed to various other pointsdepicted in FIG. 2. In one embodiment, at least 50, at least 70, or atleast 90 weight percent of the alcohols removed from the treated ionicliquid mixture can be routed to various other points in the processdepicted in FIG. 2. In one optional embodiment, at least a portion ofthe alcohols in line 194 can be routed to randomization zone 151 to beemployed as a randomizing agent. In another optional embodiment, atleast a portion of the alcohols in line 194 can be routed toprecipitation zone 152 to be employed as a precipitating agent. In yetanother optional embodiment, at least a portion of the alcohols in line194 can be routed to wash zone 154 to be employed as a wash liquid.

In one embodiment, at least a portion of the water separated from thetreated ionic liquid mixture can optionally be removed from ionic liquidrecovery/treatment zone 160 via line 192. Optionally, at least a portionof the water removed from ionic liquid recovery/treatment zone 160 canbe routed to modification zone 110 to be employed as a modifying agent.At least about 5, at least about 20, or at least 50 weight percent ofthe water separated from the treated ionic liquid mixture can optionallybe routed to modification zone 110. Additionally, at least a portion ofthe water in line 192 can optionally be routed to a waste watertreatment process.

After alcohol and/or water removal, the above-mentioned recycledcarboxylated ionic liquid can comprise residual carboxylic acid in anamount in the range of from about 0.01 to about 25 weight percent, inthe range of from about 0.05 to about 15 weight percent, or in the rangeof from 0.1 to 5 weight percent based on the entire weight of therecycled carboxylated ionic liquid. Additionally, the recycledcarboxylated ionic liquid can comprise sulfur in an amount of less than200 ppmw, less than 100 ppmw, less than 50 ppmw, or less than 10 ppmw.Furthermore, the recycled carboxylated ionic liquid can comprise halidesin an amount less than 200 ppmw, less than 100 ppmw, less than 50 ppmw,or less than 10 ppmw. Moreover, the carboxylated ionic liquid cancomprise transition metals in an amount less than 200 ppmw, less than100 ppmw, less than 50 ppmw, or less than 10 ppmw.

In one embodiment, at least a portion of the recycled carboxylated ionicliquid produced in ionic liquid recovery/treatment zone 160 canoptionally be routed to dissolution zone 120. At least 50 weightpercent, at least 70 weight percent, or at least 90 weight percent ofthe recycled carboxylated ionic liquid produced in ionic liquidrecovery/treatment zone 160 can be routed to dissolution zone 120.

In dissolution zone 120, the recycled carboxylated ionic liquid can beemployed either individually or combined with the carboxylated ionicliquid entering dissolution zone 120 via line 164 to thereby form theabove-described cellulose dissolving ionic liquid. In one embodiment,the recycled carboxylated ionic liquid can make up in the range of fromabout 10 to about 99.99 weight percent, in the range of from about 50 toabout 99 weight percent, or in the range of from about 90 to about 98weight percent of the cellulose dissolving ionic liquid in dissolutionzone 120.

Further information concerning ionic liquids, their use in theproduction of cellulose esters and cellulose derivatives, the use ofcosolvents with ionic liquids in processes to produce cellulose estersand cellulose derivatives, and treatment of cellulose esters aredisclosed in U.S. patent application entitled “Cellulose Esters andTheir Production In Carboxylated Ionic Liquids” filed on Feb. 13, 2008and having Ser. No. 12/030,387; U.S. patent application entitled“Cellulose Esters and Their Production in Halogenated Ionic Liquidsfiled on Aug. 11, 2008 and having Ser. No. 12/189,415 and itsContinuation-In-Part Application entitled “Regioselectively SubstitutedCellulose Esters Produced In A Halogenated Ionic Liquid Process andProducts Produced Therefrom” filed on Sep. 12, 2009; U.S. patentapplication “Production of Ionic Liquids” filed on Feb. 13, 2008 havingSer. No. 12/030,425; and U.S. patent application entitled “Reformationof Ionic Liquids” filed on Feb. 13, 2008 having Ser. No. 12/030,424;U.S. patent application entitled “Treatment of Cellulose Esters” filedon Aug. 11, 2008, having Ser. No. 12/189,421; U.S. patent applicationentitled “Production of Cellulose Esters In the Presence of A Cosolvent”filed on Aug. 11, 2008 having Ser. No. 12/189,753; U.S. Applicationentitled “Cellulose Solutions Comprising TetraalkylammoniumAlkylphosphates and Products Produced Therefrom” filed on Sep. 12, 2009;U.S. application entitled “Regioselectively Substituted Cellulose EstersProduced In A Tetraalkylammonium Alkylphosphate Ionic Liquid Process andProducts Produced Therefrom” filed on Sep. 12, 2009; and U.S.Provisional Application entitled “Regioselectively Substituted CelluloseEsters and Their Production in Ionic Liquids” filed on Aug. 13, 2008having Ser. No. 61/088,423; and U.S. Provisional Application entitled“Tetraalkylammonium Alkylphosphates” filed on Apr. 15, 2009 having Ser.No. 61/169,560; all of which are incorporated by reference to the extentthey do not contradict the statements herein.

This invention can be further illustrated by the following examples ofembodiments thereof, although it will be understood that these examplesare included merely for purposes of illustration and are not intended tolimit the scope of the invention unless otherwise specificallyindicated.

EXAMPLES Materials Used in Examples

Commercial grades of ionic liquids employed in the following exampleswere manufactured by BASF and were obtained through Fluka. These ionicliquids were used both as received and after purification as describedin the examples. Experimental alkyl imidazolium carboxylates were alsoprepared as described in the examples. Cellulose was obtained fromAldrich. The degree of polymerization of the Aldrich cellulose (DP ca.335) was determined capillary viscometry using copper ethylenediamine(Cuen) as the solvent. Prior to dissolution in ionic liquids, thecellulose was typically dried for 14-18 h at 50° C. and 5 mm Hg, exceptin cases where the cellulose was modified with water prior todissolution.

The relative degree of substitution (RDS) at C₆, C₃, and C₂ in thecellulose ester of the present invention was determined by carbon 13 NMRfollowing the general methods described in “Cellulose Derivatives”, ACSSymposium Series 688, 1998, T. J. Heinze and W. G. Glasser, Editors,herein incorporated by reference to the extent it does not contradictthe statements herein. Briefly, the carbon 13 NMR data was obtainedusing a JEOL NMR spectrometer operating at 100 MHz or a Bruker NMRspectrometer operating at 125 MHz. The sample concentration was 100mg/mL of DMSO-d₆. Five mg of Cr(OAcAc)₃ per 100 mg of sample were addedas a relaxation agent. The spectra were collected at 80° C. using apulse delay of 1 second. Normally, 15,000 scans were collected in eachexperiment. Conversion of a hydroxyl to an ester results in a downfieldshift of the carbon bearing the hydroxyl and an upfield shift of acarbon gamma to the carbonyl functionality. Hence, the RDS of the C₂ andC₆ ring carbons were determined by direct integration of the substitutedand unsubstituted C₁ and C₆ carbons. The RDS at C₃ was determined bysubtraction of the sum of the C₆ and C₂ RDS from the total DS. Thecarbonyl RDS was determined by integration of the carbonyl carbons usingthe general assignments described in Macromolecules, 1991, 24,3050-3059, herein incorporated by reference to the extent it does notcontradict the statements herein. In the case of cellulose mixed esterscontaining a plurality of acyl groups, the cellulose ester was firstconverted to fully substituted cellulose mixed p-nitrobenzoate ester.The position of the p-nitrobenzoate esters indicate the location of thehydroxyls in the cellulose mixed ester.

Color measurements were made following the general protocol of ASTMD1925. Samples for color measurements were prepared by dissolving 1.7 gof cellulose ester in 41.1 g of n-methylpyrrolidone (NMP). A HunterLabColor Quest XE colorimeter with a 20 mm pathlength cell operating intransmittance mode was used for the measurements. The colorimeter wasinterfaced to a standard computer running EasyMatch QC Software(HunterLab). Values (L*; white to black, a*; +red to −green, b*; +yellowto −blue) were obtained for NMP (no cellulose ester) and for thecellulose ester/NMP solutions. Color difference (E*) between the solventand the sample solutions were then calculated(E*=[(Δa*)²+[(Δb*)²+[(ΔL*)²]^(0.5) where Δ is the value for the samplesolutions minus the value for the solvent). As the value for E*approaches zero, the better the color.

Viscosity measurements were made using an AR2000 rheometer (TAInstruments LTD) interfaced with a computer running TA InstrumentsAdvantage Software. The 25 mm aluminum stage for the rheometer wasenclosed in a plastic cover with a nitrogen purge to ensure that thesamples did not pick up moisture during the measurements. The ionicliquid-cellulose solutions were prepared by the general methodsdisclosed in the examples.

Solvent casting of film was performed according to the following generalprocedure: Cellulose ester solids and 10 wt % plasticizer were added toa 90/10 wt % solvent mixture of CH₂Cl₂/methanol (or ethanol) to give afinal concentration of 5-30 wt % based on cellulose ester+plasticizer.The mixture was sealed, placed on a roller, and mixed for 24 hours tocreate a uniform solution. After mixing, the solution was cast onto aglass plate using a doctor blade to obtain a film with the desiredthickness. Casting was conducted in a fume hood with relative humiditycontrolled at 50%. After casting, the film and glass were allowed to dryfor one hour under a cover pan (to minimize rate of solventevaporation). After this initial drying, the film was peeled from theglass and annealed in a forced air oven for 10 minutes at 100° C. Afterannealing at 100° C., the film was annealed at a higher temperature(120° C.) for another 10 minutes.

Film optical retardation measurements were made using a J.A. WoollamM-2000V Spectroscopic Ellipsometer having a spectral range of 370 to1000 nm. RetMeas (Retardation Measurement) program from J.A. WoollamCo., Inc. was used to obtain optical film in-plane (R_(e)) andout-of-plane (R_(th)) retardations. Values are reported at 589 or 633 nmat a film thickness of 60 μm.

Example 1 Preparation of Cellulose Ester (Comparative)

A 3-neck 100 mL round bottom flask, fitted with two double neck adaptersgiving five ports, was equipped for mechanical stirring, with an iC10diamond tipped IR probe (Mettler-Toledo AutoChem, Inc., Columbia, Md.,USA), and with an N₂/vacuum inlet. To the flask was added 61 g of1-butyl-3-methylimidazolium chloride. Prior to adding the [BMIm]Cl, theionic liquid was melted at 90° C. then stored in a desiccator; duringstorage, the [BMIm]Cl remained a liquid. While stirring rapidly, beganadding 3.21 g of previously dried microcrystalline cellulose (DP ca.335) in small portions (3 min addition). The slurry was stirred for 5min before applying vacuum. After ca. 3 h 25 min, most of the cellulosehad dissolved except for a few small pieces and 1 large piece stuck tothe probe. After 5.5 h, the oil bath temperature was increased to 105°C. to speed up dissolution of the remaining cellulose. The solution wasmaintained at 105° C. for 1.5 h (47 min heat up) before allowing thesolution to cool to room temperature (6 h 25 min from the start of thecellulose addition) and stand overnight at ambient temperature.

After standing overnight, the cellulose/[BMIm]Cl solution was clear andthe IR spectra indicated that all of the cellulose was dissolved. Thesolution was heated to 80° C. before adding 10.11 g (5 eq) Ac₂O dropwise (26 min addition). The reaction was sampled throughout the reactionperiod by removing 6-10 g aliquots of the reaction mixture andprecipitating in 100 mL of MeOH. The solid from each aliquot was washed2× with 100 mL portions of MeOH then 2× with 100 mL of MeOH containing8% of 35 wt % H₂O₂ before drying at 60° C., 5 mm Hg. The 1^(st) samplewas white, the 2^(nd) sample was tan, and the 3^(rd) sample was brown.During the course of the reaction, the solution became progressivelydarker. Approximately 2 h 45 min after the start of the Ac₂O addition,the viscosity of the reaction mixture abruptly increased then thereaction mixture completely gelled. The oil bath was lowered and thecontact solution was allowed to cool to room temperature.

FIG. 3 is a plot of absorbance versus time for Example 1 and it showsthe dissolution of cellulose (1046 cm⁻¹) and the removal of residualwater (1635 cm⁻¹) from the mixture during the course of the dissolution.The spikes in the cellulose trend line are due to large cellulose gelparticles sticking to the probe which, are removed by the stirringaction. Clumping occurs because the surfaces of the cellulose particlesbecome partially dissolve before dispersion is obtained leading toclumping and large gel particles. The dip in the trend lines near 6 hresult from the temperature increase from 80 to 105° C. This figureillustrates that ca. 6 h is required to fully dissolve the cellulosewhen the cellulose is added to the ionic liquid that is preheated to 80°C.

FIG. 4 is a plot of absorbance versus time for Example 1 and itillustrates the acetylation of cellulose (1756, 1741, 1233 cm⁻¹), theconsumption of Ac₂O (1822 cm⁻¹), and the coproduction of acetic acid(1706 cm⁻¹) during the experiment. The DS values shown in FIG. 4 weredetermined by NMR spectroscopy and correspond to the samples removedduring the course of the contact period. As illustrated, ca. 75% of theacetylation occurred during the first hour after which the reactionrates slowed. Approximately 2 h 45 from beginning the Ac₂O addition(DS=2.45), the solution viscosity suddenly increased followed bygellation of the contact mixture. At this point, no further reactionoccurred and the remaining contact solution was processed as describedabove. It should be noted that there was still a large excess of Ac₂O atthe point of gellation. Furthermore, during the course of the contactperiod, the solution became progressively darker and the final productcolor was dark brown. Color measurements of the final sample dissolvedin NMP gave a L* value of 82.74, an a* value of 2.23, a b* value of56.94, and an E* value of 59.55. In addition to determining the DS ofeach sample, the molecular weight of each sample was determined by GPC(Table 1, below). In general, Mw was approximately 55,000 and thepolydispersity ranged from 3-4. Based on the DP of the startingcellulose, this analysis indicates that the molecular weight of thecellulose polymer remained essentially intact during the contact period.

Example 2 Modification of Cellulose with Water

A 3-neck 100 mL round bottom flask, fitted with two double neck adaptersgiving five ports, was equipped for mechanical stirring, with an iC10diamond tipped IR probe, and with an N₂/vacuum inlet. To the flask wasadded 64.3 g of 1-butyl-3-methylimidazolium chloride. Prior to addingthe [BMIm]Cl, the IL was melted at 90° C. then stored in a desiccator;the [BMIm]Cl remained a liquid during storage. To the ionic liquid wasadded 3.4 g (5 wt %) of microcrystalline cellulose (DP ca. 335) atambient temperature while stirring rapidly to disperse the cellulose.Approximately 12 min after adding the cellulose, a preheated 80° C. oilbath was raised to the flask. After ca. 17 min in the 80° C. oil bath,visually, all of the cellulose appeared to be dissolved. After ca. 22min in the 80° C. oil bath, began applying vacuum. To insure completeremoval of water, 50 min after applying vacuum, the oil bath setting wasincreased to 105° C. and the solution was stirred for 2 h 25 min beforethe oil bath was allowed to cool to room temperature.

The temperature of the clear, amber cellulose solution was adjusted to80° C. before adding 6.42 g of Ac₂O (3 eq) drop wise (5 min addition).The contact mixture was sampled throughout the reaction period byremoving 6-10 g aliquots of the contact mixture and precipitating in 100mL of MeOH. The solid from each aliquot was washed 1× with 100 mL ofMeOH then 2× with MeOH containing 8 wt % 35% H₂O₂. The samples were thendried at 60° C., 5 mm Hg overnight. During the course of the contactperiod, the color of the solution became darker ultimately becoming darkbrown. Approximately 2 h 10 min from the start of Ac₂O addition, thesolution viscosity began to increase significantly; 10 min later thesolution completely gelled out and started climbing the stir shaft. Theexperiment was aborted and MeOH was added to the flask to precipitatethe remaining product.

The precipitation and the wash liquids from each aliquot were combinedand concentrated invacuo at 68° C. until the vacuum dropped to 24 mm Hgwhich provided 54.2 g of recovered [BMIm]Cl. Analysis by ¹H NMR revealedthat the ionic liquid contained 4.8 wt % acetic acid when measured bythis technique.

FIG. 5 is a plot of absorbance versus time for Example 2 and it showsthe dissolution of cellulose (1046 cm⁻¹) and the removal of residualwater (1635 cm⁻¹) from the mixture during the course of the dissolution.As can be seen, the dissolution of the cellulose was very rapid (17 minversus 360 min in Example 1). This was due to adding the cellulose tothe ionic liquid at room temperature, stirring to get a good dispersion(higher surface area), then heating to effect dissolution. Normally,[BMIm]Cl is a solid that melts at ca. 70° C. However, if water or acarboxylic acid is allowed to mix with [BMIm]Cl, the [BMIm]Cl willremain a liquid at room temperature thus allowing introduction of thecellulose at ambient temperature. As can be seen from the water loss inFIG. 5, the [BMIm]Cl contained significant water. This exampleillustrates that the addition of water to an ionic liquid followed bycellulose addition and good mixing to get a good dispersion providesrapid dissolution of cellulose.

FIG. 6 is a plot of absorbance versus time for Example 2 and itillustrates the acetylation of cellulose (1756, 1741, 1233 cm⁻¹), theconsumption of Ac₂O (1822 cm⁻¹), and the coproduction of acetic acid(1706 cm⁻¹) during the experiment. The DS values shown in FIG. 6 weredetermined by NMR spectroscopy and correspond to the samples removedduring the course of the contact period. Relative to Example 1, thereaction rate was slower (Example 1, DS=2.44 @ 165 min; Example 2,DS=2.01 @ 166 min, cf. Table 1, below). As was observed in Example 1,the solution viscosity suddenly increased followed by gellation of thecontact mixture, but in Example 2, gellation occurred at a lower DS.Both the slower reaction rate and gellation at a lower temperature canbe attributed to the use of less Ac₂O. However, it should be noted thatthere was still a large excess of Ac₂O at the point of gellation. Aswith Example 1, during the course of the contact period, the solutionbecame progressively darker and the final product color was dark brown.Color measurements of the final sample dissolved in NMP gave a L* valueof 67.30, an a* value of 17.53, a b* value of 73.35, and an E* value of82.22. In addition to determining the DS of each sample, the molecularweight of each sample was determined by GPC (Table 1, below). Ingeneral, Mw was approximately 55,000 and the polydispersity ranged from3-6. Based on the DP of the starting cellulose, this analysis indicatesthat the molecular weight of the cellulose polymer remained essentiallyintact during the contact period.

Example 3 MSA Secondary Component, No Modification with Water

Cellulose (3.58 g, 5 wt %) was dissolved in 68 g of [BMIm]Cl in a mannersimilar to Example 2. To the cellulose solution (contact temperature=80°C.) was added a mixture of 433 mg MSA and 6.76 g of Ac₂O (3 eq) dropwise (8 min). The reaction was sampled throughout the reaction period byremoving 6-10 g aliquots of the reaction mixture and precipitating in100 mL of MeOH. The solid from each aliquot was washed 2× with 100 mLportions of MeOH then dried at 60° C., 5 mm Hg. The solid samples weresnow white. After ca. 2 h, all of the Ac₂O appeared to be consumed byIR. The experiment was aborted and the remaining sample was processed asabove.

The precipitation and the wash liquids from each aliquot were combinedand concentrated invacuo at 68° C. until the vacuum dropped to 24 mm Hgwhich provided 64 g of recovered [BMIm]Cl. Unlike Example 2, analysis by¹H NMR revealed that the ionic liquid did not contain any acetic acidwhen measured by this technique. This result indicates that MSA aids inthe removal of residual acetic acid from the ionic liquid, probably byconversion of the residual acetic acid to methyl acetate.

FIG. 7 is a plot of absorbance versus time for Example 3 and itillustrates the acetylation of cellulose (1756, 1741, 1233 cm⁻¹), theconsumption of Ac₂O (1822 cm⁻¹), and the coproduction of acetic acid(1706 cm⁻¹) during the experiment. The DS values shown in FIG. 7 weredetermined by NMR spectroscopy and correspond to the samples removedduring the course of the contact period. What is apparent from FIG. 7 isthat the rates of reaction are much faster compared to Examples 2 and 3.For example, 55 min was required to reach a DS of 1.82 in Example 1-1(Table 1, below) while only 10 min was required to reach a DS of 1.81 inExample 3-1. Similarly, 166 min was required to reach a DS of 2.01 inExample 2-4 (Table 1, below) while only 20 min was required to reach aDS of 2.18 in Example 3-2. Additionally, FIG. 7 shows that no gellationoccurred during the course of the experiment. In fact, throughout theexperiment, there was not any increase in solution viscosity, thesolution color was essentially unchanged from the initial solutioncolor, and the products isolated from the contact mixture were allwhite. Color measurements of the final sample dissolved in NMP gave a L*value of 97.65, an a* value of −2.24, a b* value of 11.07, and an E*value of 11.54. Comparison of these values to those obtained in Example1 and 2 (E*=59.55 and 82.22, respectively) shows that inclusion of asecondary component such as MSA in the contact mixture significantlyimproves solution and product color. This effect is particularlypronounced in view of the fact that the samples in Examples 1 and 2 werebleached and the samples in this Example were not bleached. As discussedin Example 36, bleaching can significantly improve product color forcellulose esters prepared from cellulose dissolved in ionic liquids.Finally, it should be noted in Table 1, below, that the Mw (ca. 40,000)for the samples of Example 3 are less than those for Examples 1 and 2and that the polydispersity (Mw/Mn) is lower and more narrow (2-3) thanthose for Examples 1 and 2 (3-6). When compared to Examples 1 and 2,Example 3 shows that inclusion of a secondary component such as MSA inthe contact mixture accelerates the rates of reaction, significantlyimproves solution and product color, prevents gellation of the contactmixture, allows the achievement of high DS values while using lessacylating reagent, and helps to promote lowering of the cellulose estermolecular weight.

TABLE 1 Properties of Cellulose Acetates Prepared Without WaterModification Example Time (min) DS Mw Mw/Mn 1-1 55 1.82 59243 3.29 1-2122 2.25 61948 4.34 1-3 165 2.44 51623 3.73 2-1 6 0.64 50225 2.93 2-2 341.49 56719 3.48 2-3 56 1.73 64553 5.4 2-4 166 2.01 66985 5.7 2-5 1762.05 63783 5.83 3-1 10 1.81 41778 1.92 3-2 20 2.18 43372 2.01 3-3 272.39 41039 2.22 3-4 43 2.52 41483 2.4 3-5 66 2.62 40412 2.54 3-6 1242.72 39521 2.55

Example 4 Modification with Water, MSA Secondary Component

A 3-neck 100 mL round bottom flask, fitted with two double neck adaptersgiving five ports, was equipped for mechanical stirring, with an iC10diamond tipped IR probe, and with an N₂/vacuum inlet. To the flask added58.07 g of 1-butyl-3-methylimidazolium chloride. Prior to adding the[BMIm]Cl, the IL was melted at 90° C. then stored in a desiccator. Theflask was placed in an oil bath and heated to 80° C.

To 3.06 g (5 wt %) of microcrystalline cellulose (DP ca. 335), was added3.06 g of water. The slurry was hand mixed and allowed to stand for ca.30 min before adding the slurry in small portions to the [BMIm]Cl (5 minaddition). This gave a hazy solution in which the cellulose wassurprisingly well dispersed. The slurry was stirred for 27 min, beforeapplying vacuum. Visually, after 28 min under vacuum all of thecellulose had dissolved which was confirmed by IR. By IR, there wasstill ca. 3 wt % water in the [BMIm]Cl when all of the cellulose wasdissolved. The system was maintained under vacuum at 80° C. to removethe remaining water. The sample was allowed to cool to room temperatureand left standing until the next step.

The cellulose solution was heated to 80° C. before adding a mixture of5.78 g Ac₂O (3 eq) and 368 mg MSA drop wise (8 min). The reaction wassampled throughout the reaction period by removing 6-10 g aliquots ofthe reaction mixture and precipitating in 100 mL of MeOH. The solid fromeach aliquot was washed 2× with 100 mL portions of MeOH then dried at60° C., 5 mm Hg. The isolated samples were snow white. The solutioncolor was excellent through out the experiment and there was noindication of a viscosity increase. After ca. 2 h 25 min, infraredspectroscopy indicated that all of the Ac₂O was consumed. The experimentwas aborted and the remaining sample was processed as above.

FIG. 8 is a plot of absorbance versus time for Example 4 and it showsthe dissolution of cellulose (1046 cm⁻¹) and the removal of residualwater (1635 cm⁻¹) from the mixture during the course of the dissolution.As can be seen, the dissolution of the water wet (activated) cellulosewas very rapid (28 min) despite the presence of a significant amount ofwater. This is surprising in view of the conventional teachings. Theaddition of water wet cellulose to the ionic liquid enables one toobtain a good dispersion of cellulose with little clumping. Uponapplication of a vacuum to remove the water, the cellulose rapidlydissolves without clumping to form large particles.

FIG. 9 is a plot of absorbance versus time for Example 4 and itillustrates the acetylation of cellulose (1756, 1741, 1233 cm⁻¹), theconsumption of Ac₂O (1822 cm⁻¹), and the coproduction of acetic acid(1706 cm⁻¹) during the experiment. The DS values shown in FIG. 9 weredetermined by NMR spectroscopy and correspond to the samples removedduring the course of the contact period. Relative to Example 3, thereaction rate to produce cellulose acetate was similar. However, themolecular weights (ca. 33,000) of the cellulose acetate samples (Table2, below) were notably lower that that observed in Example 3 and muchlower than that observed in Examples 1 and 2 (Table 1, above).Additionally, the polydispersities for the samples of Example 4 are allless than 2, less than that observed for the samples of Examples 1, 2,and 3.

This example illustrates that water wet cellulose leads to goodcellulose dispersion in the ionic liquid and rapid cellulosedissolution. The reaction rate for formation of cellulose acetate israpid. Surprisingly, water wet cellulose leads to lower molecular weightcellulose acetate with low polydispersities relative to dry cellulose.The cellulose acetate made from water wet cellulose has better acetonesolubility relative to when dry cellulose is utilized.

Example 5 Modification with Water, MSA Secondary Component

A 3-neck 100 mL round bottom flask, fitted with two double neck adaptersgiving five ports, was equipped for mechanical stirring, with a iC10diamond tipped IR probe, and with an N₂/vacuum inlet. To the flask added67.33 g of 1-butyl-3-methylimidazolium chloride. Prior to adding the[BMIm]Cl, the IL was melted at 90° C. then stored in a desiccator. Theflask was placed in an oil bath and heated to 80° C. To 7.48 g (10 wt %)of microcrystalline cellulose (DP ca. 335), was added 7.08 g of water.The cellulose slurry was hand mixed and allowed to stand for ca. 60 minbefore adding the slurry in small portions to the [BMIm]Cl (8 minaddition). This gave a hazy solution in which the cellulose wassurprisingly well dispersed. The slurry was stirred for 10 min, beforeapplying vacuum. The cellulose dissolution was left stirring overnight.

Infrared spectroscopy indicated that essentially all of the cellulosewas dissolved within 50 min after applying vacuum; ca. 3.5 h wasrequired to remove the water. To the cellulose solution was added amixture of 14.13 g of Ac₂O (3 eq) and 884 mg (0.2 eq) of MSA drop wise(11 min). The reaction was sampled throughout the reaction period byremoving 6-10 g aliquots of the reaction mixture and precipitating in100 mL of MeOH. The solid from each aliquot was washed 2× with 100 mLportions of MeOH then dried at 60° C., 5 mm Hg. The isolated sampleswere snow white. The solution color was excellent throughout theexperiment and there was no indication of a viscosity increase. Afterca. 2 h 10 min, all of the Ac₂O appeared to be consumed by IR. Theexperiment was aborted and the remaining sample was processed as above.

FIG. 10 is a plot of absorbance versus time for Example 5 and it showsthe dissolution of cellulose (1046 cm⁻¹) and the removal of residualwater (1635 cm⁻¹) from the mixture during the course of the dissolution.As can be seen, the dissolution of the water wet (activated) cellulosewas very rapid (50 min) despite the presence of a significant amount ofwater and the increase in cellulose concentration relative to Example 4.

FIG. 11 is a plot of absorbance versus time for Example 5 and itillustrates the acetylation of cellulose (1756, 1741, 1233 cm⁻¹), theconsumption of Ac₂O (1822 cm⁻¹), and the coproduction of acetic acid(1706 cm⁻¹) during the experiment. The DS values shown in FIG. 11 weredetermined by NMR spectroscopy and correspond to the samples removedduring the course of the contact period. Despite the increase incellulose concentration, relative to Examples 3 and 4, the reaction rateto produce cellulose acetate was similar. The molecular weights (ca.22,000) of the cellulose acetate samples (Table 2, below) were notablylower that that observed in Example 4 and much lower than that observedin Examples 1, 2, and 3 (Table 1, above). As was observed for Example 4,the polydispersities for the samples of Example 5 are all less than 2,less than that observed for the samples of Examples 1, 2, and 3.

This example illustrates that water wet cellulose leads to goodcellulose dispersion in the ionic liquid and rapid cellulose dissolutioneven when the cellulose concentration is increased to 10 wt %. Thereaction rate for formation of cellulose acetate is rapid. Surprisingly,water wet cellulose at this concentrations leads to even lower molecularweight cellulose acetates with low polydispersities relative to drycellulose. The cellulose acetate made from water wet cellulose hasbetter acetone solubility relative to when dry cellulose is utilized.

Example 6 Modification with Water, MSA Secondary Component

A 3-neck 100 mL round bottom flask, fitted with two double neck adaptersgiving five ports, was equipped for mechanical stirring, with an iC10diamond tipped IR probe, and with an N₂/vacuum inlet. To the flask added51.82 g of 1-butyl-3-methylimidazolium chloride. Prior to adding the[BMIm]Cl, the IL was melted at 90° C. then stored in a desiccator. Theflask was placed in an oil bath and heated to 80° C. To 9.15 g (15 wt %)of microcrystalline cellulose (DP ca. 335), added 53.6 g of water. Afterhand mixing, the cellulose was allowed to stand in the water for 50 minbefore filtering which gave 18.9 g of a wet cellulose cake. The waterwet cellulose was then added in small portions to the [BMIm]Cl (5 minaddition). Within 2 min, the cellulose was finely dispersed in the ionicliquid. Ten minutes after adding the cellulose to the [BMIm]Cl, theflask was placed under vacuum. After ca. 1 h, there were no visiblecellulose particles; the solution viscosity was very high and thesolution started climbing the stir rod. The solution was left stirringovernight at 80° C. under vacuum.

Infrared spectroscopy indicated that ca. 1 h was required for cellulosedissolution and 2 h was required to strip the water to the initialvalue. The cellulose solution was heated to 100° C. prior to adding amixture of 17.28 g Ac₂O (3 eq) and 1.087 g (0.2 eq) of MSA drop wise (8min). The reaction was sampled throughout the reaction period byremoving 6-10 g aliquots of the reaction mixture and precipitating in100 mL of MeOH. The solid from each aliquot was washed 1× with 100 mL ofMeOH then 2× with MeOH containing 8 wt % 35% H₂O₂. The solid sampleswere then dried at 60° C., 5 mm Hg. After ca. 65 min, all of the Ac₂Oappeared to be consumed by IR. The experiment was aborted and theremaining sample was processed as above.

FIG. 12 is a plot of absorbance versus time for Example 6 and it showsthe dissolution of presoaked water wet cellulose (1046 cm⁻¹) and theremoval of residual water (1635 cm⁻¹) from the mixture during the courseof the dissolution. As can be seen, the dissolution of the water wet(activated) cellulose was very rapid (60 min) despite the presence of asignificant amount of water and the use of 15 wt % cellulose. Even moresurprising was the rapid removal of water (ca. 2 h) at this highcellulose concentration.

FIG. 13 is a plot of absorbance versus time for Example 6 and itillustrates the acetylation of cellulose (1756, 1741, 1233 cm⁻¹), theconsumption of Ac₂O (1822 cm⁻¹), and the coproduction of acetic acid(1706 cm⁻¹) during the experiment. The DS values shown in FIG. 13 weredetermined by NMR spectroscopy and correspond to the samples removedduring the course of the contact period. Despite the increase incellulose concentration (15 wt %), acetic anhydride could be easilymixed into the cellulose solution at 100° C. The higher reactiontemperature led to an increase in reaction rate. Again, the molecularweights (ca. 20,000) of the cellulose acetate samples (Table 2, below)were notably lower that that observed in Examples 1, 2, and 3 (Table 1,above) were the cellulose was dried prior to use; the polydispersitiesfor the samples of Example 6 are also less than 2.

This example illustrates that water wet cellulose leads to goodcellulose dispersion in the ionic liquid and rapid cellulose dissolutioneven when the cellulose concentration is increased to 15 wt %. Thisexample also shows that higher temperature (100° C.) increases reactionrates for formation of cellulose acetate. Surprisingly, water wetcellulose at this concentrations leads to even lower molecular weightcellulose acetates with low polydispersities relative to dry cellulose.The cellulose acetate made from water wet cellulose has better acetonesolubility relative to when dry cellulose is utilized.

TABLE 2 Effect of Water Modification on Properties of Cellulose AcetatesExample Time (min) DS Mw Mw/Mn 4-1 9 1.58 31732 1.73 4-2 13 1.94 335591.64 4-3 21 2.15 34933 1.63 4-4 35 2.28 31810 1.77 4-5 150 2.63 307711.89 5-1 11 1.95 24522 1.6 5-2 14 2.21 23250 1.67 5-3 18 2.35 22706 1.765-4 22 2.52 22692 1.79 5-5 31 2.59 21918 1.86 5-6 45 2.60 21628 1.89 5-770 2.66 19708 1.97 5-8 130 2.67 20717 1.99 6-1 10 2.63 20729 1.67 6-2 142.75 19456 1.78 6-3 18 2.80 19658 1.84 6-4 23 2.87 18966 1.84 6-5 322.89 20024 1.88 6-6 65 2.96 18962 1.85

Example 7 Miscible Cosolvent

A 3-neck 100 mL round bottom flask, fitted with two double neck adaptersgiving five ports, was equipped for mechanical stirring, with an iC10diamond tipped IR probe, and with an N₂/vacuum inlet. To the flask added58.79 g of 1-butyl-3-methylimidazolium chloride. Prior to adding the[BMIm]Cl, the IL was melted at 90° C. then stored in a desiccator. Theflask was placed in an oil bath and heated to 80° C. After reaching 80°C., began collecting IR spectra before adding 1.82 g (3 wt %) of glacialacetic acid. The mixture was stirred for 12 min before adding 10.38 g(15 wt %) cellulose (DP ca. 335) as a water wet cellulose cake (10.29 gwater, prepared by soaking the cellulose for 50 min in excess water, 9min addition). The mixture was stirred for ca. 9 min to allow thecellulose to disperse before applying a vacuum. After ca. 65 min,infrared spectroscopy indicated that all of the cellulose was dissolved(FIG. 14). Stirring was continued for an additional 70 min before adding1.82 g of glacial acetic acid (6 wt % total). In order to reduce thesolution viscosity, the stirring was turned off 8 min after adding theacetic acid and the oil bath temperature was increased to 100° C. Afterreaching 100° C. (45 min) stirring was resumed. Infrared spectroscopyindicated that upon resuming stirring, the acetic acid mixed well withthe cellulose solution. The final solution was clear and no celluloseparticles were observed. After standing for 10 days, the cellulosesolution was still clear and could be hand stirred at room temperaturewhich one cannot do with a 15 wt % cellulose solution in [BMIm]Cl in theabsence of acetic acid.

This example shows that significant amount of a miscible cosolvent suchas a carboxylic acid compatible with cellulose acylation can be mixedwith a cellulose-ionic liquid sample while still maintaining cellulosesolubility. A cosolvent has the added benefit of reducing solutionviscosity.

Example 8 Randomization

A 3-neck 250 mL round bottom flask, fitted with two double neck adaptersgiving five ports, was equipped for mechanical stirring, with an iC10diamond tipped IR probe, and with an N₂/vacuum inlet. To the flask added149.7 g of 1-butyl-3-methylimidazolium chloride. The flask was placed inan oil bath and heated to 80° C. Microcrystalline cellulose (12.14 g,7.5 wt %, DP ca. 335) was added to 68.9 g of water. After hand mixing,the cellulose was allowed to stand in the water for 45 min at 60° C.before filtering which gave 24.33 g of a wet cellulose cake. The waterwet cellulose was then added in small portions to the [BMIm]Cl (5 minaddition). Approximately 15 min after adding the cellulose to the[BMIm]Cl, the flask was placed under vacuum by gradually lowering thevacuum starting at ca. 120 mm Hg to ca. 1.4 mm Hg. After ca. 85 min,there were no visible cellulose particles; IR spectroscopy indicatedthat all of the cellulose was dissolved. The solution was left stirringovernight at 80° C. under vacuum.

To the cellulose solution heated to 80° C. was added a mixture of 22.93g Ac₂O (3 eq) and 1.427 g (0.2 eq) of MSA drop wise (15 min). Thereaction was sampled throughout the reaction period by removing 6-10 galiquots of the reaction mixture and precipitating in 100 mL of MeOH.The solid from each aliquot was washed 3× with 100 mL portions of MeOHthen dried at 60° C., 5 mm Hg. After removing an aliquot 192 min fromthe start of the Ac₂O addition, 1.21 g of MeOH was added to the contactmixture. The contact mixture was stirred for an addition 120 min beforeadding 1.95 g of water. The contact mixture was then stirred overnightat 80° C. (14 h 40 min) at which time, the experiment was aborted andthe remaining sample was processed as above.

The contact times, DS and molecular weights for isolated samples removedfrom the contact mixture are summarized below in Table 3.

TABLE 3 Effect of Randomization on Cellulose Acetates Example Time (min)DS Mw Mw/Mn 8-1 16 1.95 26492 1.54 8-2 18 2.15 24838 1.57 8-3 21 2.2423973 1.63 8-4 25 2.33 23043 1.7 8-5 32 2.42 23499 1.79 8-6 57 2.5621736 1.82 8-7 190 2.73 20452 2.08 8-8 After MeOH Addition 2.73 204782.00  8-10 After H₂O Addition 2.59 21005 1.89

With increasing contact time, the DS increased (until water was added)and the Mw decreased. Fifty-seven minutes after starting the contactperiod, the cellulose acetate sample had a DS of 2.56 and a Mw of21,736. Prior to adding the MeOH/water, the DS was 2.73 and the Mw was20,452. After the water contact period, the isolated cellulose acetatehad a DS of 2.59 a Mw of 21,005 indicating that the DS was reduced butthe Mw was unchanged.

FIG. 15 shows the proton NMR spectra of a cellulose acetate prepared bydirect acetylation (DS=2.56) and after randomization (DS=2.59). Both thering protons attached to the anhydroglucose monomers and acetyl protonsattached to the acetyl substituents are shown. FIG. 15 demonstrates thateven though these two cellulose acetates have much essentially the sameDS, they have a much different monomer content.

Example 9 MSA Secondary Component, Minimal Acylating Reagent

A 3-neck 100 mL round bottom flask, fitted with two double neck adaptersgiving five ports, was equipped for mechanical stirring, with an iC10diamond tipped IR probe, and with an N₂/vacuum inlet. To the flask added60.47 g of 1-allyl-3-methylimidazolium chloride. The flask was placed inan oil bath and heated to 80° C. Microcrystalline cellulose (9.15 g, 7wt %, DP ca. 335) was added to 27.3 g of water. After hand mixing, thecellulose was allowed to stand in the water for 50 min at 60° C. beforefiltering which gave 9.44 g of a wet cellulose cake. The water wetcellulose was then added in small portions to the [AMIm]Cl (5 minaddition). Approximately 15 min after adding the cellulose to the[AMIm]Cl, the flask was placed under vacuum by gradually lowering thevacuum starting at ca. 120 mm Hg. After ca. 40 min, there were novisible cellulose particles; IR spectroscopy indicated that all of thecellulose was dissolved. The solution was left stirring overnight at 80°C. under vacuum.

To the cellulose solution heated to 80° C. was added a mixture of 8.58 gAc₂O (3 eq) and 537 mg (0.2 eq) of MSA drop wise (5 min). The reactionwas sampled throughout the reaction period by removing 6-10 g aliquotsof the reaction mixture and precipitating in 100 mL of MeOH. The solidfrom each aliquot was washed 3× with 100 mL portions of MeOH then driedat 60° C., 5 mm Hg. After all of the Ac₂O appeared to be consumed by IR,the experiment was aborted and the remaining sample was processed asabove.

The contact times, DS and molecular weights for isolated samples removedfrom the contact mixture are summarized below in Table 4.

TABLE 4 Contact Times and Properties of Cellulose Acetate Prepared in[AMIm]Cl. Example Time (min) DS Mw Mw/Mn 9-1 5 1.74 36192 1.69 9-2 82.24 35734 1.84 9-3 11 2.38 32913 1.9 9-4 15 2.48 31811 1.99 9-5 24 2.6031970 2.14 9-6 50 2.74 31302 2.36 9-7 109 2.82 30808 2.48

Five minutes after starting the reaction, the first cellulose acetatesample had a DS of 1.74 and a Mw of 36,192. With increasing contacttime, the DS increased and the Mw decreased. After 109 min, the DS was2.82 and the Mw was 30,808. This example shows that, compared to theconventional method of Example 11 (5 eq Ac₂O, 6.5 h contact time), themethod of Example 9 provides for a higher DS and a significant reductionin cellulose acetate molecular weight. For example, the conventionalmethod of Example 11 requires 6.5 h to provide a cellulose acetate witha DS of 2.42 and a Mw of 50,839 while in Example 9, a cellulose acetatewith a DS of 2.48 and a Mw of 31,811 was achieved in 15 min.

Example 10 Conventional Cellulose Ester Preparation (Comparative)

A solution of cellulose (5 wt %) dissolved in 29.17 g of [BMIm]Cl washeated to 80° C. with an oil bath. The solution was held under vacuum(ca. 7 mm Hg) while stirring for 2 h. To the cellulose solution wasadded 4.6 g (5 eq) of Ac₂O (5 min addition). During the course of thereaction, the solution color became gradually darker (brown). After 2.5h, the solution had gelled so the contact solution was allowed to coolto room temperature. The product was isolated by adding the solution towater then homogenizing to give a dispersed gel/powder. The mixture wasfiltered and washed extensively with water. After drying the solidinvacuo at 50° C., 2.04 g of a pink powder was obtained that wasinsoluble in acetone. Analysis by ¹H NMR indicated that the sample had aDS of 2.52 and a Mw of 73,261.

Example 11 Conventional Cellulose Ester Preparation (Comparative)

To a 3-neck 100 mL round bottom flask equipped for mechanical stirringand with an N₂/vacuum inlet added 33.8 g of 1-allyl-3-methylimidazoliumchloride. While stirring rapidly, added 1.78 g of dry cellulose powder(DP ca. 335). The flask was placed under vacuum (2 mm Hg) and themixture was stirred at room temperature to insure that the cellulose waswell dispersed. After 15 min, the cellulose was well dispersed and thesolution viscosity was rising. The flask was placed in an oil bath whichwas heated to 80° C. After 40 min, all of the cellulose was dissolved.The solution was maintained at 80° C. for 6.5 h before allowing thesolution to cool to room temperature and stand overnight.

The viscous solution was heated to 80° C. before adding 5.6 g (5 eq) ofAc₂O drop wise (15 min). After 5 h, the product was isolated by pouringthe mixture into 300 mL of MeOH. The MeOH/solid slurry was stirred forca. 30 min before filtering to remove the liquids. The solid was thentaken up in two 200 mL portions of MeOH and the slurry was stirred forca. 30 min before filtering to remove the liquids. The solids were driedovernight at 55° C. (6 mm Hg) which gave 2.27 g of a powder that gave ahazy acetone solution. Analysis by ¹H NMR and by GPC indicated that thesample had a DS of 2.42 and a Mw of 50,839.

Example 12 MSA Secondary Component, Long Chain Aliphatic CelluloseEsters

A solution of cellulose (5 wt %) dissolved in [BMIm]Cl was heated to 80°C. with an oil bath. The solution was held under vacuum (ca. 2.5 mm Hg)while stirring for 4 h. To the cellulose solution was added a mixture of10.88 g (5 eq) of nonanoic anhydride and 141 mg of MSA (25 minaddition). After 18.5 h, the solution was allowed to cool to roomtemperature before it was poured into a solution of 80:20 MeOH:H₂O.After filtering the solid was washed extensively with 85:15 MeOH:H₂Othen with 95:5 MeOH:H₂O. The sample was dried invacuo which gave 3.7 gof a white powder soluble in isododecane. Analysis by ¹H NMR indicatedthat the product was cellulose nonanoate with a DS of 2.49.

Obtainment of a cellulose nonanoate with a high degree of substitutionby the method of this example is surprising in view of conventionalteachings that long chain aliphatic cellulose esters with a DS greaterthan ca. 1.5 cannot be prepared in ionic liquids.

Example 13 MSA Secondary Component, C3 and C4 Aliphatic Cellulose Esters

A solution of cellulose (5 wt %) dissolved in [BMIm]Cl was heated to 80°C. with an oil bath. The solution was held under vacuum (ca. 6 mm Hg)while stirring overnight. To the cellulose solution was added a mixtureof 7.91 g (5 eq) of butyric anhydride and 190 mg of MSA (25 minaddition). After 2.6 h, the solution was allowed to cool to roomtemperature before it was poured into water. The solid was washedextensively with water before drying invacuo which gave 2.62 g of awhite powder soluble in acetone and 90:10 CHCl₃:MeOH. Analysis by ¹H NMRindicated that the product was cellulose butyrate with a DS of 2.59.

This example shows that C3 and C4 aliphatic cellulose esters with highdegrees of substitution can be prepared by the methods of this example.

Example 14 Homogenization of Cellulose Solution

To a 1 L flat bottom kettle was added 193.6 g of solid [BMIm]Cl. A 3neck top was placed on the kettle and the kettle was fitted with aN₂/vacuum inlet and for mechanical stirring. The kettle was then placedin an 80° C. oil bath and the [BMIm]Cl was melted while stirring under a6 mm Hg vacuum. After the [BMIm]Cl was completely melted, 10.2 g ofpreviously dried cellulose (DP ca. 335) was added and the mixture washomogenized with a Heidolph Silent Crusher. After ca. 3 min ofhomogenization, essentially all of the cellulose was dissolved. Thesolution was stirred under vacuum (6 mm Hg) for an additional 1.5 h atwhich time, all of the cellulose was dissolved.

This example illustrates that high intensity mixing can be used todisperse the cellulose (increased surface area) which leads to rapidcellulose dissolution.

Example 15 Acetone Solubility

The solubilities of cellulose acetate in acetone were evaluated asfollows: Acetone (Burdick & Jackson high purity grade) was dried priorto use using 4A molecular sieves (purchased from Aldrich and stored inan oven at 125° C.). All of the cellulose acetates were dried prior touse in a vacuum oven (Eurotherm 91e) at 60° C., 5 mm Hg for at least 12h. Each cellulose acetate was weighed into a 2 Dram vial (100 mg±1 mg)and 1 mL±5 μL of dry acetone was then added to the vial (vials wereobtained from VWR). The vials were then placed in an ultrasonic bath(VWR, model 75HT) and ultrasonicated at room temperature for 30-120 minthen removed and vortexed (VWR minivortexer) at room temperature using aspeed setting of 10. If the cellulose acetate appeared to be dissolvingbut the rate of dissolution appeared to be slow, the vial was placed ona roller and mixed (ca. 15 revolutions per min) overnight at ambienttemperature. Following the mixing period, the solubility of eachcellulose acetate was rated as follows:

Rating Description 1 Soluble, transparent with no visible particles 2Partially soluble, hazy 3 Partially soluble, very hazy, visibleparticles 4 Gel 5 Swollen solid 6 InsolubleCellulose acetates with a rating of 1 are very useful in allapplications in which acetone solubility or solubility in relatedsolvents (e.g. diethyl phthalate) is a critical factor (e.g. solventspinning of acetate fiber or melt processing of plasticized celluloseacetate). Cellulose acetates with a rating of 2 or 3 would requireadditional filtration to remove insoluble particles and/or the use ofco-solvents before they would have utility. Cellulose acetates with arating of 4-6 would not have utility in these applications. Hence,cellulose acetates with a rating of 1 are highly desired.

The solubility in acetone of cellulose acetates prepared in Examples3-6, 8, 9 are compared (Table 5, below) to the solubilities of thecellulose acetates in Examples 1, 2 and to cellulose acetates (Examples15-1 to 15-6) prepared by traditional methods. The cellulose acetatesprepared by traditional methods were prepared by acetylation ofcellulose to make cellulose triacetate followed by H₂SO₄ catalyzedreduction of DS, a process know to yield cellulose acetates that arerandom copolymers. In the absence of water (dry acetone), the acetonesolubility of these cellulose acetates is known to be limited to anarrow range (from about 2.48 to about 2.52).

TABLE 5 Solubility of Cellulose Acetate in Acetone (100 mg/mL). ExampleDS Solubility 1-1 1.82 5 1-2 2.25 4 1-3 2.44 4 2-1 0.64 5 2-2 1.49 5 2-31.73 5 2-4 2.01 5 2-5 2.05 5 3-1 1.81 5 3-2 2.18 1 3-3 2.39 1 3-4 2.52 23-5 2.62 3 3-6 2.72 3 4-1 1.58 6 4-2 1.94 2 4-3 2.15 1 4-4 2.28 1 4-52.63 2 5-1 1.95 2 5-2 2.21 1 5-3 2.35 1 5-4 2.52 2 5-5 2.59 2 5-6 2.60 25-7 2.66 3 5-8 2.67 3 6-1 2.63 2 6-2 2.75 3 6-3 2.80 3 6-4 2.87 3 6-52.89 3 6-6 2.96 3 8-1 1.95 3 8-2 2.15 1 8-3 2.24 1 8-4 2.33 1 8-5 2.42 18-6 2.56 2 8-7 2.73 2 9-1 1.74 5 9-2 2.24 1 9-3 2.38 1 9-4 2.48 2 9-52.60 3 9-6 2.74 3 9-7 2.82 3 15-1  2.48 1 15-2  2.46 2 15-3  2.16 315-4  1.99 5 15-5  1.96 5 15-6  1.80 6

Careful examination of Table 5 reveals that the cellulose acetateshaving a DS from about 2.42 to about 2.15 that were produced byacetylation of cellulose dissolved in ionic liquids in the presence of asecondary component (Examples 3-6, 8, 9) all have a acetone solubilityrating of 1. That is, all of these samples yield transparent acetonesolutions in which there are no visible particles. In contrast,cellulose acetates produced by acetylation of cellulose dissolved inionic liquids in the absence of a secondary component (Examples 1 and 2)have acetone solubility ratings of 4-5 regardless of DS. For example,Example 1-2 (no secondary component) has a DS of 2.25 and this celluloseacetate forms a gel in acetone while Examples 8-3 and 9-2 (includessecondary component) have a DS of 2.24 and these cellulose acetatesyield transparent acetone solutions. In agreement with what is knownabout cellulose acetates prepared by traditional methods, only one ofthe cellulose acetates examined (15-1, DS=2.48) has an acetonesolubility rating of 1. Example 15-3 (DS=2.16) has an acetone solubilityrating of 3 as opposed to Examples 4-3 and 8-2 (DS=2.15) which haveacetone solubility ratings of 1.

This example shows that cellulose acetates produced by acetylation ofcellulose dissolved in ionic liquids in the presence of a secondarycomponent having a DS of about 2.4 to about 2.1 yield transparentacetone solutions. In the absence of a secondary component, none of thecellulose acetates yield transparent acetone solutions. Furthermore, theDS range that yield transparent acetone solutions when using celluloseacetates produced by acetylation of cellulose dissolved in ionic liquidsin the presence of a secondary component is broader and lower relativeto cellulose acetates produced by traditional methods. Without wishingto be bound by theory, the evidence indicates that these solubilitydifferences reflect a difference in copolymer compositions.

Example 16 Purification of [BMIm]acetate

To a 1 L 3-neck round bottom flask was added 360 mL of water, 1.30 g ofacetic acid, and 5.68 g of Ba(OH)₂.H₂O. The mixture was heated to 80° C.giving a translucent solution. To this solution was added 300 g ofcommercial [BMIm]OAc dropwise (1 h addition) containing 0.156 wt %sulfur as determined by XRF. The solution was held at 80° C. for anaddition hour before allowing the solution to cool to room temperature.The solids formed during the reaction were removed by centrifugingbefore concentration the solution in vacuo (60-65° C., 20-80 mm Hg) to apale yellow liquid. The liquid was extracted with two 300 mL portions ofEtOAc. The liquid was concentrated first at 60° C., 20-50 mm Hg then at90° C., 4 mm Hg leading to 297.8 g of a pale yellow oil. Proton NMRconfirmed the formation of the [BMIm]OAc which, by XRF, contained 0.026wt % sulfur.

Example 17 Preparation of [BMIm]propionate

To a 1 L 3-neck round bottom flask was added 400 mL of water, 62.7 g ofacetic acid, and 267 g of Ba(OH)₂.H₂O. The mixture was heated to 74° C.giving a translucent solution. To this solution was added 100 g ofcommercial [BMIm]HSO₄ dropwise (1.75 h addition). The solution was heldat 74-76° C. for an addition 30 min before allowing the solution to coolto room temperature and stand overnight (ca. 14 h). The solids formedduring the reaction were removed by filtration before concentration thesolution in vacuo which gave an oil containing solids which formedduring concentration. The solids were removed centrifuging giving anamber liquid. Additional product was obtained by slurring the solids inEtOH and centrifuging. The liquids were concentrated first at 60° C.,20-50 mmHg then at 90° C., 4 mm Hg leading to 65.8 g of an amber oil.Proton NMR confirmed the formation of the [BMIm]OPr which, by XRF,contained 0.011 wt % sulfur.

Example 18 Preparation of [BMIm]formate

To 300 mL autoclave was added 25 g of 1-butylimidazole, 45.4 g (3.75 eq)of methyl formate, and 21 mL of MeOH (2.58 eq). The autoclave waspressurized to 1035 kPa before heating the solution to 150° C. Thecontact solution was maintained at 150° C. for 18 h. The solution wasallowed to cool to room temperature before removing the volatilescomponents in vacuo. Proton NMR of the crude reaction mixture revealedthat 89% of the 1-butylimidazole was converted to [BMIm]formate.Purified [BMIm]formate was obtained by removal of 1-butylimidazole fromthe crude product by distillation.

Example 19 Conversion of [BMIm]formate to [BMIm]acetate Using MethylAcetate

To 300 mL autoclave was added 25 g of [BMIm]formate, 50.3 g (5.0 eq) ofmethyl acetate, and 50 mL of MeOH (9 eq). The autoclave was pressurizedto 1035 kPa before heating the solution to 170° C. The contact solutionwas maintained 170° C. for 15.3 h. The solution was allowed to cool toroom temperature before removing the volatiles components in vacuo.Proton NMR of the reaction mixture revealed that 57% of the[BMIm]formate was converted to [BMIm]acetate.

Example 20 Conversion of [BMIm]formate to [BMIm]acetate Using AceticAnhydride

To 25 mL single-neck round bottom flask was added 11.1 g of[BMIm]formate. Acetic anhydride (6.15 g) was added dropwise to the[BMIm]formate. Evolution of gas was noted during the addition as well aswarming of the solution (47° C.). The flask was then placed in apreheated 50° C. water bath for 45 min before applying a vacuum (4 mmHg) and heating to 80° C. to remove the volatile components. Analysis ofthe resulting liquid by 1H NMR indicated 100% conversion of the startingmaterial to [BMIm]acetate.

Example 21 Conversion of [BMIm]formate to [BMIm]acetate Using AceticAcid

To 300 mL autoclave was added 25 g of [BMIm]formate, 87.4 g (6.3 eq) ofacetic acid, and 23.1 g of MeOH (5.3 eq). The autoclave was pressurizedto 1035 kPa before heating the solution to 150° C. The contact solutionwas maintained 150° C. for 14 h. The solution was allowed to cool toroom temperature before removing the volatiles components in vacuo.Proton NMR of the reaction mixture revealed that 41% of the[BMIm]formate was converted to [BMIm]acetate.

Example 22 Conversion of [BMIm]acetate to [BMIm]formate Using MethylFormate

To 1 L autoclave was added 100.7 g of [BMIm]acetate, 152.5 g (5 eq) ofmethyl formate, and 200 mL of MeOH (9.7 eq). The autoclave waspressurized to 1035 kPa before heating the solution to 140° C. Thecontact solution was maintained 140° C. for 18 h. The solution wasallowed to cool to room temperature before removing the volatilescomponents in vacuo. Proton NMR of the reaction mixture revealed that100% of the [BMIm]acetate was converted to [BMIm]formate.

Example 23 Comparison of High and Low Sulfur [BMIm]OAc 23A:

To a 100 mL 3-neck round bottom flask was added 32.75 g of commercialhigh sulfur [BMIm]OAc (0.156 wt % sulfur) and 1.72 g of cellulosepowder. This mixture was briefly homogenized at ambient temperaturebefore the flask was placed in a preheated 80° C. oil bath. The mixturewas stirred at 80° C., 2 mm Hg for 1.75 h; ca. 15 min was required tocompletely dissolve the cellulose. The straw colored solution wasallowed to cool to room temperature and stand under vacuum overnight(ca. 14 h).

To the mechanically stirred solution was added a solution of methanesulfonic acid (MSA, 210 mg) and acetic anhydride (5.42 g, 5 eq/AGU)dropwise (23 min). At the end of the addition, the temperature of thecontact mixture was 35° C. and the solution was dark amber. After 1.5 hfrom the start of the addition, 5.5 g of the contact mixture was removedand the product was isolated by precipitation in MeOH. The contactmixture was then heated to 50° C. (25 min heat up time) and stirred for1.5 h before 6.5 g of solution was removed and poured into MeOH. Theremaining contact solution was heated to 80° C. (25 min heat up) andstirred for 2.5 h before pouring into MeOH. All of the solids obtainedby precipitation in MeOH were isolated by filtration, washed extensivelywith MeOH, and dried overnight at 50° C., 5 mm Hg.

23B:

An identical reaction to 23A was conducted side-by-side using 37.02 g oflow sulfur [BMIm]OAc (0.025 wt % sulfur, cf. example 1), 1.95 g ofcellulose, 6.14 g of acetic anhydride, and 222 mg of MSA.

The grams of product isolated and the analysis of each product issummarized below in Table 6.

TABLE 6 Yield and Properties of CA Prepared in [BMIm]OAc Entry Yield (g)DS Mn Mw Mz 23A-RT 0.37 2.53 15123 54139 135397 23A-50° C. 0.45 2.6512469 51688 123527 23A-80° C. 1.36 2.62 15828 85493 237785 23B-RT 0.290.80 14499 65744 301858 23B-50° C. 0.40 0.80 14768 57066 227833 23B-80°C. 1.26 0.76 16100 70293 325094

As can be seen from Table 6, above, the DS of the CA made using the highsulfur [BMIm]OAc as solvent was higher and the molecular weight lowerrelative to the CA made using the low sulfur [BMIm]OAc as solvent.Despite the increased temperature and extended contact time, the DS didnot increase significantly above that observed after 1.5 h contact timeat room temperature regardless of which [BMIm]OAc was used as thesolvent. Another notable feature of this example was the color of thesolutions and products. The contact solution involving high sulfur[BMIm]OAc solvent was black at all temperatures while the contactsolution involving low sulfur [BMIm]OAc solvent retained the straw colortypical of these solutions prior to the addition of the anhydride. TheCA solids obtained from the high sulfur [BMIm]OAc solvent were brown toblack in appearance while the CA solids obtained from the low sulfur[BMIm]OAc solvent were white and provided colorless solutions upondissolution in an appropriate solvent.

This example shows that impurities (e.g., sulfur or halides) in the highsulfur [BMIm]OAc can act as a catalyst in the esterification ofcellulose dissolved in the [BMIm]OAc. However, the same impuritiesnegatively impact the molecular weight and quality of the product insuch a manner that the CA does not have practical value. When celluloseis dissolved in [BMIm]OAc containing no or little of these impurities,high-quality CA can be obtained. By introduction of an appropriatecatalyst, high quality CA with the desired DS can be obtained in apredictable manner.

Example 24 Acetylation of Cellulose in High Chloride [EMIm]OAc

Cellulose (1.19 g) was dissolved in 22.65 g of commercial [EMIm]OAcwhich, by XRF, contained 0.463 wt % chloride following the generalprocedure described in Example 8 with the exception that the mixture wasnot homogenized prior to heating to 80° C.

To the mechanically stirred straw colored solution preheated to 80° C.was added a solution of MSA (141 mg) and acetic anhydride (3.76 g, 5eq/AGU) dropwise (10 min). By the end of the addition, the contactmixture became dark brown-black. The contact solution was stirred for2.5 h before pouring into H₂O. The resulting solids were isolated byfiltration, washed extensively with H₂O, and dried overnight at 50° C.,5 mm Hg. This yielded 1.57 g of a brown-black CA powder. Analysisrevealed that the CA had a DS of 2.21 and that the Mw was 42,206.

This example shows that [EMIm]OAc containing high levels of halides isnot a suitable solvent for esterification of cellulose.

Example 25 Acetylation of Cellulose in [BMIm]CI and [BMIm]OAc 25A:

Previously dried cellulose (13.2 g) and solid [BMIm]Cl (250.9 g, mp=70°C.) were combined in a glass jar. The glass jar was placed in apreheated 40° C. vacuum oven and heated to 80° C. over 3 h. The samplewas allowed to stand under vacuum at 80° C. for ca. 14 h before the jarwas removed. The sample was immediately homogenized giving a clearsolution of cellulose.

To a 100 mL 3-neck round bottom flask was added 33.6 g of the cellulosesolution prepared above. The flask was placed in a preheated 80° C. oilbath and a vacuum was applied (7-8 mm Hg). The solution was then stirredfor 21 h while at 80° C. and under vacuum. The cellulose solution wasthen allowed to cool to 38° C.; the temperature could not be loweredfurther due to the solution viscosity. Acetic anhydride (5.3 g, 5eq/AGU) was added dropwise over 7 min. The contact mixture was thenstirred at 32-35° C. for 2 h before a small amount of the solution wasremoved and poured into MeOH resulting in precipitation of the celluloseacetate. The remaining contact mixture was then heated to 50° C. andheld at that temperature for 1.6 h before removing a small amount of thesolution which was poured into MeOH to precipitate the celluloseacetate. The remaining contact mixture was then heated to 80° C. andheld at that temperature for 1.5 h before allowing the solution to cooland adding 60 mL of MeOH to precipitate the cellulose acetate. All threesamples were washed extensively with MeOH then dried at 50° C., 5 mm Hgovernight.

25B:

To a 100 mL 3-neck round bottom flask was added 31.3 g of the cellulosesolution prepared above. The same general protocol as used in theprevious reaction was followed with the exception that Zn(OAc)₂ (0.05eq/AGU) was added to the cellulose solution prior to cooling to 38° C.

25C:

To a 100 mL 3-neck round bottom flask was added 27.41 g of low sulfur[BMIm]OAc liquid (cf. example 16) and 1.44 g of cellulose. The flask wasplaced in a preheated 80° C. oil bath and the mixture was allowed tostir overnight (ca. 14 h) under a 2 mm Hg vacuum.

After cooling the solution to room temperature (25.1° C.), Ac₂O (5eq/AGU) was added to the cellulose solution dropwise (25 min addition).The contact mixture was stirred for 1.8 h at room temperature beforeremoving a small portion of the solution which was poured into MeOH toprecipitate the cellulose acetate. The remaining contact mixture washeated to 50° C. and maintained at that temperature for 1.5 h beforeremoving a small portion of the solution which was poured into MeOH toprecipitate the cellulose acetate. The remaining contact mixture washeated to 80° C. and maintained at that temperature for 2.5 h beforecooling and pouring into MeOH. All three samples were washed extensivelywith MeOH then dried at 50° C., 5 mm Hg overnight.

25D:

To a 100 mL 3-neck round bottom flask was added 25.55 g of low sulfur[BMIm]OAc liquid (cf. example 16) and 1.35 g of cellulose. The flask wasplaced in a preheated 80° C. oil bath and the mixture was allowed tostir overnight (ca. 14 h) under a 2 mm Hg vacuum. The same generalprotocol as used in the previous reaction was followed with theexception that Zn(OAc)₂ (0.05 eq/AGU) was added to the cellulosesolution prior to cooling to room temperature.

Analysis of the cellulose acetates isolated from these 4 comparativereactions (25A-25D) is summarized below in Table 7.

TABLE 7 Physical properties of CA prepared in [BMIm]Cl or [BMIm]OAcEntry Solvent Catalyst DS Mn Mw Mz 25A-RT [BMIm]Cl none 0.57 7753 1677732019 25A-50° C. [BMIm]Cl none 1.42 9892 19083 33019 25A-80° C. [BMIm]Clnone 2.27 11639 21116 34138 25B-RT [BMIm]Cl Zn(OAc)₂ 1.77 8921 1946836447 25B-50° C. [BMIm]Cl Zn(OAc)₂ 2.32 7652 18849 38367 25B-80° C.[BMIm]Cl Zn(OAc)₂ 2.75 7149 18964 38799 25C-RT [BMIm]OAc none 1.17 703941534 118265 25C-50° C. [BMIm]OAc none 1.17 7839 45116 136055 25C-80° C.[BMIm]OAc none 1.17 7943 48559 165491 25D-RT [BMIm]OAc Zn(OAc)₂ 2.278478 47730 125440 25D-50° C. [BMIm]OAc Zn(OAc)₂ 2.30 11017 53181 13661925D-80° C. [BMIm]OAc Zn(OAc)₂ 2.34 12096 56469 141568

This comparative example illustrates a number of important points. Inthe case of [BMIm]Cl, the DS of the cellulose acetate increases witheach contact time-temperature from 0.57 to 2.27. The same trend isobserved with [BMIm]Cl+Zn(OAc)₂ with the exception that the DS at eachcontact time-temperature is higher due to the Zn(OAc)₂ which acts as acatalyst. In the case of [BMIm]OAc, with or without Zn(OAc)₂, the DSdoes not significantly change from that obtained at room temperaturewith increasing contact time-temperature; the total DS is significantlyincreased by the action of the Zn(OAc)₂. This unexpected observationindicates that acetylation of cellulose dissolved in [BMIm]OAc is muchfaster at lower temperatures relative to that observed in acetylation ofcellulose dissolved in [BMIm]Cl. It should also be noted that atransition metal like Zn is very effective in catalyzing or promotingthe acylation of cellulose dissolved in ionic liquids. Finally, itshould also be noted that the molecular weights of the celluloseacetates obtained by acetylation of cellulose dissolved in [BMIm]OAc issignificantly greater relative to when cellulose is dissolved in[BMIm]Cl.

Example 26 Preparation of Mixed Cellulose Esters

The following general procedure was used to prepare cellulose mixedesters. To a 100 mL 3-neck round bottom flask was added the desiredamount of 1-butyl-3-methylimidazolium carboxylate. While stirring atroom temperature, 5 wt % cellulose was slowly added to the ionic liquid.After the cellulose was dispersed in the ionic liquid, the flask wasplaced under vacuum (2-5 mm Hg) and the contact mixture was heated to80° C. The contact solution was then stirred for ca. 2 h before adding0.1 eg/AGU of Zn(OAc)₂. The contact solution was stirred for ca. 30 minbefore the solution was allowed to cool to room temperature and standovernight (ca. 14 h).

The contact solution was placed under N₂ before the dropwise addition of5 eq/AGU of the desired carboxylic anhydride. When the addition wascomplete, the flask was placed in a preheated 40° C. oil bath. Thecontact mixture was stirred for 5 h before the solution was allowed tocool and poured into MeOH. The resulting solids were isolated byfiltration, washed extensively with MeOH, and dried in vacuo (50° C., 5mm Hg). The products were characterized by ¹H NMR and the results aresummarized below in Table 8.

TABLE 8 Cellulose Esters Prepared in Different Alkyl ImidazoliumCarboxylates Entry Ionic liquid Anhydride DS_(Total) DS_(Ac) DS_(Pr)DS_(Bu) 1 [BMIm]OAc Bu₂O 2.40 2.43 — 0.45 2 [BMIm]OBu Ac₂O 2.43 2.30 —0.70 3 [BMIm]OPr Bu₂O 2.52 — 1.95 1.05

Note that in Table 8, above, the DS of the individual substituents havebeen normalized to 3.0 for comparison purposes. As this exampleillustrates, when cellulose is dissolved in an alkyl imidazoliumcarboxylate and contacted with an carboxylic anhydride different fromthe anion of the ionic liquid, the product is a cellulose mixed ester.That is, the cellulose substituents come from the added anhydride andfrom the alkyl imidazolium carboxylate. In effect, the alkyl imidazoliumcarboxylate is acting as an acyl donor.

Example 27 Removal of Carboxylic Acid

To each vessel of a 4 vessel Multimax high pressure reactor equippedwith an in situ infrared probe was added previously dried [BMIm]OAc, 1molar equivalent of acetic acid based on ionic liquid, different molaramounts of MeOH based on acetic acid, and optionally, a catalyst (2 mol%). The pressure in each vessel was increased to 5 bar over a 3 minperiod before the contact temperature was increased to 140° C. over a 25min period. The contact mixtures were then held at 140° C. for 10-15 hand the reaction in each vessel was monitored by infrared spectroscopy.The vessels were allowed to cool to 25° C. over a 30 min period. Thecontents of each vessel were then concentrated invacuo to remove allvolatile components before analyzing each sample by proton NMR. FIG. 16shows a plot of wt % acetic acid versus time as determined by infraredspectroscopy; the final concentration of acetic acid was confirmed by ¹HNMR. FIG. 16 shows that in all cases, the reactions were complete within9-10 h. The most significant factor affecting the rates and extend ofreaction was the number of molar equivalents of MeOH. The wt % aceticacid remaining in the [BMIm]OAc ranged from 7.4 wt % to 2.2 wt %.

With typical distillation techniques, it is extremely difficult to getthe excess carboxylic acid concentration below 1 molar equivalent basedon carboxylated ionic liquid. In the case of acetic acid in [BMIm]OAc,this corresponds to ca. 23 wt % acetic acid. This example shows that, byconversion of the acetic acid to methyl acetate which is much moreeasily removed, the amount of residual acetic acid can be reduced wellbelow 23 wt %. The amount of acetic acid removed will depend upon theamount of acetic acid initially present, concentration of MeOH, contacttimes, and contact temperature. As shown in this example, it is notnecessary to remove all of residual carboxylic acid; in many instances,it is desirable to have residual carboxylic acid.

Example 28 Solubility of Cellulose in Ionic Liquid

Samples of 1-butyl-3-methylimmidazolium acetate containing differentamounts of acetic acid in 2 oz jars were dried at 80° C.±5°, ca. 3 mm Hgovernight (ca. 14 h). Examples 28-1 through 28-5 were prepared by themethod of Example 27. Examples 28-6 through 28-8 were prepared by addinga known amount of acetic acid to neat [BMIm]OAc (Table). Cellulose (5 wt%, DP 335), was added to each [BMIm]OAc sample and the each sample wasbriefly homogenized. Each sample was transferred to a microwave reactionvessel which was then capped with an air tight lid then placed in a 48cell microwave rotor. The rotor was placed in a Anton Paar Synthos 3000microwave and the cellulose-[BMIm]OAc mixtures were heated to 100° C.using a 3 min ramp and held for 10 min before heating to 120° C. using a3 min ramp and held for 5 min. Inspection of each vessel indicated thatthe cellulose in each example was dissolved in the [BMIm]OAc.

TABLE 9 Solubility of Cellulose in [BMIm] OAc Example wt % HOAc IL (g)Soluble 28-1 2.2 6.16 y 28-2 2.8 8.78 y 28-3 5.8 8.48 y 28-4 6.6 8.48 y28-5 7.4 8.15 y 28-6 10.0 10.23 y 28-7 12.5 10.26 y 28-8 14.5 10.18 y

This example shows that excess residual carboxylic acid in ionic liquidscan be reduced by the method of Example 27 and that the recycled ionicliquid can then be used to dissolve cellulose so that the solutions canbe used for preparing cellulose esters. This example also shows thatcellulose can be dissolved in an ionic liquid containing up to about 15wt % carboxylic acid.

Example 29 Recycling of Ionic Liquid

To a 500 mL flat bottom kettle was added 299.7 g of [BMIm]OAc. A 4-necktop was placed on the kettle and the kettle was fitted with a N₂/vacuuminlet, a React IR 4000 diamond tipped IR probe, a thermocouple, and formechanical stirring. The kettle contents were placed under vacuum (ca.4.5 mm Hg) and heated to 80° C. using an oil bath. The removal of waterfrom the [BMIm]OAc was followed by infrared spectroscopy (FIG. 17).After ca. 16 h, the oil bath was removed and the kettle contents wereallowed to cool to room temperature.

To the ionic liquid was added 3.77 g of Zn(OAc)₂. The mixture wasstirred for ca. 75 minutes to allow the Zn(OAc)₂ to dissolve beforeslowly adding 33.3 g (10 wt %) of previously dried cellulose (DP ca.335) over a 26 min period. The mixture was stirred at room temperaturefor ca. 4 h at which time no particles or fiber were visible in thetranslucent solution; infrared spectroscopy indicated that all of thecellulose was dissolved (FIG. 18). The solution was heated to 80° C. Bythe time the temperature reached 60° C., the translucent solution wascompletely clear. After reaching 80° C., the solution was cooled to roomtemperature.

To the cellulose-[BMIm]OAc solution was added 104.9 g of Ac₂O (5 eq)dropwise over a 70 min period. During the Ac₂O addition, the contacttemperature rose from an initial value of 21.4° C. to a maximum value of44.7° C. Infrared spectroscopy indicated that the Ac₂O was consumednearly as fast as it was added (FIG. 19). When all of the Ac₂O wasadded, the contact temperature immediately began to decline and thecontact mixture went from a fluid liquid to a flaky gel. Stirring wascontinued for an additional 3.5 h but no changes were observed byinfrared spectroscopy.

The gel was then added to 800 mL of MeOH while stirring resulting in theprecipitation of a white powder. After separation by filtration, thesolids were then washed 3 times with ca. 800 mL portions of MeOH then 1time with ca. 900 mL of MeOH containing 11 wt % of 35 wt % H₂O₂. Thesolids were then dried at 40° C., 3 mm Hg resulting in 60.4 g of a whitesolid. Analysis by proton NMR and GPC revealed that the solid was acellulose triacetate (DS=3.0) having a Mw of 58,725. The cellulosetriacetate (13.6 wt %) was completely soluble in 90/10 CH₂Cl₂/MeOH fromwhich clear films can be cast. Such films are useful in constructingliquid crystalline displays and in photographic film base.

The precipitation and wash liquids from the cellulose triacetateisolation were concentrated invacuo at 50° C. until the vacuum droppedto ca. 3 mm Hg which gave 376.6 g of a liquid. Proton NMR showed thatthe liquid was [BMIm]OAc containing ca. 17 wt % excess acetic acid. To a1.8 L autoclave was added the 376.8 g of recovered [BMIm]OAc along with483.8 g of MeOH. The pressure in autoclave was adjusted to 100 psi withN₂ before the vessel contents were heated to 140° C. and held for 9 h.After cooling to room temperature, the volatile components were removedinvacuo which gave 299.8 g of a liquid. Proton NMR showed the liquid tobe [BMIm]OAc containing 2.6 wt % excess acetic acid. When the weight ofthe initial [BMIm]OAc is corrected for water content, the amount ofrecycled [BMIm]OAc corresponds to 100% recovery.

This example shows that cellulose triacetate can rapidly be preparedfrom cellulose dissolved in ionic liquids. This example also shows thatexcess carboxylic acid can be removed from the ionic liquid and therecycled ionic liquid can be recovered in high yield. The recycled ionicliquid can then be used to dissolve cellulose so that the solutions canbe used again for preparing cellulose esters.

Example 30 Anion Exchange to Form Carboxylated Ionic Liquid

To a vial containing a small magnetic stir bar was added 4.2 g of[BMIm]formate. An iC10 diamond tipped IR probe was inserted into thevial so that the reaction could be monitored in situ by infraredspectroscopy. To the [BMIm]formate was added 0.5 eq of Ac₂O in oneportion. As FIGS. 20 and 21 show, 50% of the [BMIm]formate wasimmediately converted to [BMIm]OAc. Additional spectra were collected toallow the system to stabilize before adding another 0.5 eq of Ac₂O inone portion. Infrared spectroscopy indicated that the remaining[BMIm]formate was immediately converted to [BMIm]OAc.

This example shows that [BMIm]formate is rapidly converted to [BMIm]OAcwith the addition of Ac₂O. The reaction rate is so rapid that the[BMIm]formate can be titrated with Ac₂O until no gas is evolved.

Example 31 Effect of MeOH During Anion Exchange

To a vial containing a small magnetic stir bar was added 3.15 g of[BMIm]formate. An iC10 diamond tipped IR probe was inserted into thevial so that the reaction could be monitored in situ by infraredspectroscopy. To the [BMIm]formate was added 2 eq of MeOH. After thesystem thermally stabilized, 1 eq of Ac₂O was added to the [BMIm]formatein one portion. As FIGS. 22 and 23 show, infrared spectroscopy indicatedthat the [BMIm]formate was immediately converted to [BMIm]OAc.

This example shows that the reaction of [BMIm]formate with Ac₂O to form[BMIm]OAc is much faster than the reaction of Ac₂O with MeOH to formMeOAc. Hence, it is not necessary to remove MeOH from [BMIm]formateprior to converting the [BMIm]formate to [BMIm]OAc.

Example 32 Effects of Water Modification and MSA

A 3-neck 250 mL round bottom flask, fitted with two double neck adaptersgiving five ports, was equipped for mechanical stirring, with a iC10diamond tipped IR probe, and with an N₂/vacuum inlet. To the flask added62.37 g of 1-butyl-3-methylimidazolium acetate.

To 5.06 g (7.5 wt %) of cellulose (DP ca. 335) was added 20.68 g ofwater. After hand mixing, the cellulose was allowed to stand in thewater for 65 min at 60° C. before filtering which, gave 10.78 g of a wetcellulose cake. The water wet cellulose was then added in small portionsto the [BMIm]OAc (5 min addition). Within 5 min, the cellulose was welldispersed in the ionic liquid (a few small clumps were visible). Themixture was stirred for 7 min before a preheated 80° C. oil bath wasraised to the flask. The mixture was then stirred for 28 min (visually,nearly all of the cellulose was dissolved) before slowly placing theflask contents under vacuum with the aid of a bleed valve (FIG. 24).After 1.5 h, the vacuum was 1.9 mm Hg. The clear mixture was thenstirred overnight under vacuum at 80° C.

The clear solution was allowed to cool to room temperature 15 h 45 minfrom the point of cellulose addition before adding a mixture of 12.11 g(3.8 eq) of Ac₂O and 600 mg of MSA dropwise (28 min addition). Themaximum temperature reached during the Ac₂O addition was 46° C. Eightminutes after completing the Ac₂O addition, a preheated 50° C. oil bathwas raised to the flask. The mixture was stirred for 16 min before 1.46g of water was slowly added to the solution (2 min addition). Thesolution was then stirred for 17 min before adding an additional 0.47 gof water. The solution was then stirred for 5 h 9 min before cooling thesolution to room temperature. The reaction was sampled (FIG. 25)throughout the contact period by removing 6-10 g aliquots of thereaction mixture and precipitating in 100 mL of MeOH. The solid fromeach aliquot was washed once with a 100 mL portion of MeOH then twicewith 100 mL of MeOH containing 8 wt % of 35 wt % H₂O₂. The samples werethen dried at 60° C., 5 mm Hg overnight.

This example illustrates a number of benefits of the methods employedherein. As can be seen from FIG. 24, water wet cellulose can be readilydissolved in carboxylated ionic liquid even when a significant amount ofwater still remains in the ionic liquid. As shown in FIG. 25, the rateof reaction in the acylation of this cellulose in a carboxylated ionicliquid is very rapid; a significant concentration of Ac₂O is neverobserved indicating that the Ac₂O is consumed as fast as it is added.The rapid rates of reaction can lead to a much different monomerdistribution relative to that observed in other ionic liquids. Forexample, FIG. 26 compares the proton resonances of the protons attachedto the anhydroglucose rings of cellulose acetates (DS=2.56) preparedfrom cellulose dissolved in [BMIm]OAc (top spectrum) and dissolved in[BMIm]Cl (bottom spectrum). The major resonances in the top spectrumcentered near 5.04, 5.62, 4.59, 4.29, 4.04, 3.73, and 3.69 correspond totrisubstituted monomers. In the bottom spectrum, there are much less ofthese resonances relative to the other type of monomer resonances. Thisdiscovery is significant in that the rapid rates of reaction provide ameans to produce nonrandom cellulose ester copolymers with differentlevels of block segments. The extent and the size of the block segmentswill depends upon factors such as mixing, prior water treatment or nowater treatment of the cellulose, concentration and type of catalyst,contact temperature, and the like. As shown in FIG. 24, 3 samples weretaken prior to the addition of water. These 3 samples ranged in DS from2.48-2.56 and at 10 wt % in acetone, they were soluble giving slightlyhazy solutions (solubility rating of 2). In contrast, the 2 samplestaken after water addition (DS ca. 2.52) were insoluble in acetone(solubility rating of 6). FIG. 27 compares the ring proton resonancesfor cellulose acetates prepared from cellulose dissolved in [BMIm]OAcbefore and after addition of water. The top spectrum corresponds to acellulose acetate after water addition (DS=2.53) and the bottom spectrumcorresponds to a cellulose acetate before water addition (DS=2.56). Thedifferences between these 2 spectra are consistent with differentmonomer compositions in the copolymers.

Example 33 Production of Cellulose Triacetate

To a 3-neck 100 mL round bottom flask equipped for mechanical stirringand with an N₂/vacuum inlet added 34.63 g of 1-ethyl-3-methylimidazoliumacetate. While stirring rapidly, added 6.11 g (15 wt %) of dry cellulosepowder (DP ca. 335). The flask was placed in a 90° C. oil bath and themixture was stirred for 10 min before applying vacuum (2 mm Hg). After50 min, the oil bath temperature was increased to 100° C. After 2 h 25min, the oil bath was turned off and left the solution was left standingunder vacuum overnight.

To the cellulose solution was added a mixture of 731 mg of MSA and 19.24g (5 eq) of Ac₂O dropwise. Initially, the solution was stirred slowly sothat the solution did not bunch around the stir shaft. As the Ac₂O wasadded, the solution viscosity dropped; after adding ca. 5 mL, thesolution stirred easily and the stir rate was increased. During theaddition, the solution viscosity did not increase and no localized gelswere observed until the last few drops of Ac₂O were added (40 minaddition). At this point the entire contact mixture suddenly gelled. Thecontact temperature rose from 24.1° C. to 47.5° C. by the end ofaddition. During the addition, there was little change in the color ofthe solution. After the reaction gelled, 11.54 g of the reaction mixturewas removed with a spatula and solids were obtained by precipitation inMeOH (Sample 1). The flask containing the remaining reaction mixture wasthen placed in a preheated 50° C. oil bath. After 20 min at 50° C.,there was no evidence of the gel softening. Hence, the gel was allowedto cool to room temperature and 50 mL of MeOH was added to the flask.The flask contents were then dumped into 400 mL of MeOH which gave awhite precipitate (Sample 2). Both fractions were processed by stirringthe initial slurry for ca. 1 h before isolating the solids byfiltration. The solids were washed by taking them up in 300 mL of MeOHand stirring the slurry for ca. 1 h before the solids were isolated byfiltration. The solids were twice taken up in 300 mL of 12/1 MeOH/35%H₂O₂ and the slurry was stirred for ca. 1 h before the solids wereisolated by filtration. The solids were then dried overnight at 50° C.,ca. 20 mm Hg.

The combined yield for Sample 1 and 2 was 10.2 g of a white solid.Analysis by 1H NMR showed that Samples 1 and 2 were identical and thatthey were cellulose triacetates with a DS of 3.0. By GPC, both sampleshave a Mw of ca. 54,000.

This example shows that cellulose triacetate can rapidly be preparedfrom cellulose dissolved in [EMIm]OAc. Cellulose triacetate can be usedto prepare film useful in liquid crystalline displays and photographicfilm base.

Example 34 Immiscible Co-Solvent (Effect on IL Viscosity)

To a 3-neck 50 mL round bottom flask equipped for mechanical stirringand with an N₂/vacuum inlet added 20.03 g of 1-ethyl-3-methylimidazoliumacetate. While stirring rapidly, added 1.05 g of dry cellulose powder(DP ca. 335). The flask was placed under vacuum (2 mm Hg) and placed inan oil bath preheated to 90° C. After 1 h 45 min, the oil bathtemperature was increased to 100° C. and stirred an additional 55 min (2h 40 min total contact time) before allowing the solution to cool toambient temperature while under vacuum.

To the cellulose solution was added 20 mL of methyl acetate resulting ina 2-phase reaction mixture. While stirring rapidly, a mixture of 131 mgof MSA and 4.63 g of Ac₂O was added drop wise (10 min). The contacttemperature increased from 23.3° C. to 35.4° C. and, at the end of theaddition, the contact mixture was a single phase and the viscosity ofthe single phase was much less than that of the originalcellulose-[EMIm]OAc solution. Twenty-five minutes after beginning theaddition, the flask was placed in a preheated 50° C. oil bath. Thecontact mixture was stirred for 2 h at 50° C. before allowing thecontact mixture to cool to ambient temperature over 50 min. The productwas precipitated in 350 mL of MeOH and the slurry was stirred for ca. 1h before the solids were isolated by filtration. The solids were washedby taking them up in 300 mL of MeOH and stirring the slurry for ca. 1 hbefore the solids were isolated by filtration. Twice, the solids weretaken up in 300 mL of 12/1 MeOH/35% H₂O₂ and the slurry was stirred forca. 1 h before the solids were isolated by filtration. The solids werethen dried overnight at 50° C., ca. 20 mm Hg which gave 1.68 g of awhite solid. Analysis by ¹H NMR revealed that the solid was a celluloseacetate with a DS of 2.67. Analysis by GPC indicated that the celluloseacetate had a Mw of 51,428 and a Mw/Mn of 4.08.

This example shows that a cellulose solution in an ionic liquid can becontacted with an immiscible or sparingly soluble co-solvent withoutcausing precipitation of the cellulose. Upon contact with an acylatingreagent, the cellulose is esterified changing the solubility of the nowcellulose ester-ionic liquid solution with the formerly immiscibleco-solvent so that the contact mixture becomes a single phase. Theresulting single phase has much lower solution viscosity than theinitial cellulose-ionic liquid solution. This discovery is significantin that highly viscous cellulose solutions can be used to make celluloseesters while still maintaining the ability to mix and process thesolution. The discovery also provides a means to process highly viscouscellulose-ionic liquid solutions at lower contact temperatures. Thecellulose ester product can be isolated from the new single phase byconventional means. The cellulose ester product has desirable degrees ofsubstitution, molecular weights, and solubility in solvents such asacetone, and can be readily melt processed when plasticized withplasticizers such as diethyl phthalate and the like.

Example 35 Immiscible Co-Solvent (Biphasic to Single Phase)

A 3-neck 100 mL round bottom flask containing 28.84 g of a 5 wt %cellulose solution in [BMIm]Cl was equipped for mechanical stirring andwith an N₂/vacuum inlet. The flask was placed in a preheated 80° C. oilbath and the flask contents were placed under vacuum (ca. 7 mm Hg) for 2h. To the solution was added 25 mL of methyl ethyl ketone that had beenpreviously dried over 4A molecular sieves resulting in two well definedphases. To the biphasic mixture was added 4.54 g of Ac₂O while stirringvigorously. After ca. 75 min, the contact mixture appeared to behomogeneous. After 2.5 h, the contact mixture was allowed to cool toroom temperature. Phase separation did not occur even when a smallamount of water and methyl ethyl ketone was added to the homogeneousmixture. The product was isolated by addition of the contact mixture to200 mL of MeOH followed by filtration to separate the solids. The solidswere washed twice with MeOH and three times with water before they weredried at 50° C., ca. 5 mm Hg. Analysis by ¹H NMR and by GPC revealedthat the product was a cellulose acetate with a DS of 2.11 and Mw of50,157.

This example shows that a cellulose solution in an ionic liquid such as[BMIm]Cl can be contacted with an immiscible or sparingly solubleco-solvent such as methyl ethyl ketone without causing precipitation ofthe cellulose. Upon contact with an acylating reagent, the cellulose isesterified changing the solubility of the now cellulose ester-ionicliquid solution with the formerly immiscible co-solvent so that thecontact mixture became a single phase from which the cellulose estercould be isolated by precipitation with an alcohol.

Example 36 Color Measurements for Cellulose Esters Prepared fromCellulose Dissolved in Ionic Liquids

Color development during esterification of cellulose dissolved in ionicliquids depend upon a number of factors. These factors include the typeof ionic liquid used to dissolve the cellulose, impurities contained inthe ionic liquid, type of cellulose, the presence or absence of binarycomponents (cf. Example 3), cellulose dissolution contact time andtemperature, esterification contact time and temperature, among others.Understanding those factors and the mechanism involved in colorformation is the best means for preventing color formations. Even whenthe best practices are followed, colored product is still oftenobtained. Hence, a means for removing or minimizing the color is veryimportant. In this regard, we have found that we can minimize color bycontacting the cellulose ester with a bleaching agent while dissolved inionic liquid or after separation of the cellulose ester from the ionicliquid.

Example of a general method for bleaching cellulose esters whiledissolved in ionic liquid: To a 7.5 wt % solution of cellulose dissolvedin [BMIm]Cl was added a mixture of 2.9 eq Ac₂O and 0.1 eq MSA. After 65minutes, in situ IR indicated that the reaction was complete. To thesolution was added a bleaching agent (in this case, 0.75 wt % of a 2.25wt % solution of KMnO₄ dissolved in MeOH). The mixture was stirred for 2h before the cellulose ester was isolated by precipitation in water,washed with water, and dried. The concentration of bleaching agent andbleaching contact time depends upon the particular process.

Example of a general method for bleaching cellulose esters afterseparation from the ionic liquid: After completing the reaction, thecellulose ester is isolated from the ionic liquid by precipitation in anonsolvent such as water or alcohol. The liquids are separated from thecellulose ester and, optionally, the cellulose ester can be washedfurther before contacting the solid product with a bleaching agent (e.g.35 wt % aqueous H₂O₂). Specific examples of this process can be found inExamples 33 and 34. The concentration of bleaching agent, the number ofbleaching cycles, and bleaching contact time depends upon the particularprocess.

Values of L*, a*, b*, and E* for cellulose ester solutions before andafter bleaching are provided in Table 10. Comparing entries 1-3 toentries 4-6 (no bleaching) it is evident that more color is createdduring cellulose esterification when the anion of the ionic liquid is acarboxylate relative to when the anion is a halide. When the anion was ahalide, in the absence of bleaching L* and E* ranged from 93.6-97.7 and19.1-11.5, respectively (entries 1-3). Bleaching with H₂O₂ afterseparation of the cellulose ester from the ionic liquid increased a* anddecreased b* resulting in improvement of color which is reflected in alower E* value (entries 7 and 8). Bleaching the cellulose ester while itis dissolved in the ionic liquid led to a similar improvement in color(entry 9). In this case L* and a* increased while b* decreased resultingin an E* value of 4.85. When the anion was a carboxylate, in the absenceof bleaching L* and E* ranged from 46.6-74.5 and 108.6-89.9,respectively (entries 4-6). Bleaching with H₂O₂ after separation of thecellulose ester from the ionic liquid led to a dramatic improvement ofcolor. L* increased while a* and b* decreased resulting in E* values of0.9-11.2 (entries 10-16).

TABLE 10 Values of L*, a*, b*, and E* for cellulose ester solutionsbefore and after bleaching. Entry L* a* b* E* IL-BC CE Bleach 1 97.65−2.24 11.07 11.54 [BMIm]Cl-(MSA) CA None 2 94.28 −1.85 17.83 18.83[BMIm]Cl-(MSA) CA None 3 93.56 −1.74 17.84 19.06 [BMIm]Cl-(MSA) CA None4 46.56 41.45 77.89 103.19 [BMIm]OAc-(MSA) CA None 5 50.35 35.44 89.8108.59 [BMIm]OAc CA None 6 74.52 12.66 85.28 89.91 [BMIm]OAc CAP None 796.89 −1.44 10.10 10.68 [BMIm]Cl-(MSA) CA H₂O₂ 8 98.24 −1.09 4.37 4.85[BMIm]Cl-(MSA) CA H₂O₂ 9 98.37 −1.04 5.69 6.02 [BMIm]Cl-(MSA) CA KMnO₄10 98.43 −3.00 10.72 11.24 [EMIm]OAc CA H₂O₂ 11 98.10 −3.06 10.34 10.95[BMIm]OAc CA H₂O₂ 12 98.44 −1.51 5.87 6.27 [BMIm]OBu CAB H₂O₂ 13 97.91−2.43 10.68 11.15 [EMIm]OAc-(MSA) CA H₂O₂ 14 99.44 0.00 0.58 0.87[BMIm]OAc—(Zn(OAc)₂) CA H₂O₂ 15 99.02 0.05 1.63 1.94[BMIm]OAc—(Zn(OAc)₂) CA H₂O₂ 16 99.32 −0.48 1.98 2.16 [BMIm]OPr-(MSA) CPH₂O₂

This example illustrates that contacting a cellulose ester with ableaching agent while dissolved in ionic liquid or after separation ofthe cellulose ester from the ionic liquid can lead to very significantimprovements in color.

Example 37 Viscosity of Solutions of Cellulose Dissolved in IonicLiquids Containing Miscible Cosolvents

Solutions of cellulose dissolved in [BMIm]Cl containing different levelsof acetic acid were prepared by the following general procedure: To a3-neck 50 mL round bottom flask equipped for mechanical stirring andwith a N2/vacuum inlet was added [BMIm]Cl. The flask contents wereheated to 80° C. and placed under vacuum (0.8 mm Hg). After 1.7 h, 5 wt% acetic acid was added to the [BMIm]Cl before allowing the solution tocool to room temperature. Cellulose (5 wt %) was added to the solutionbefore heating the mixture to 80° C. The mixture was stirred until ahomogeneous solution was obtained (ca. 80 min), The solution was thencooled to room temperature.

FIG. 28 compares the viscosities of cellulose solutions containing noacetic acid, 5 wt % acetic acid, and 10 wt % acetic acid at 25, 50, 75,100° C. The viscosity of the cellulose-[BMIm]Cl-5 wt % acetic acidsolution is significantly less than that of cellulose-[BMIm]Cl at alltemperatures. For example, at 25° C. and 0.2 rad/sec the viscosity ofthe cellulose-[BMIm]Cl-5 wt % acetic acid solution is 466 poise versus44,660 poise for the cellulose-[BMIm]Cl solution. Comparing theviscosities of the cellulose-[BMIm]Cl-10 wt % acetic acid solution tothe cellulose-[BMIm]Cl-5 wt % acetic acid and cellulose-[BMIm]Clsolutions at 25° C., it is evident that the viscosity of thecellulose-[BMIm]Cl-10 wt % acetic acid solution is less than that of thecellulose-[BMIm]Cl solution but greater than that of thecellulose-[BMIm]Cl-5 wt % acetic acid solution. At 25° C. and 0.2rad/sec, the viscosities of the cellulose-[BMIm]Cl-10 wt % acetic acid,cellulose-[BMIm]Cl-5 wt % acetic acid, and cellulose-[BMIm]Cl solutionsare 22,470, 466, and 44,660 poise, respectively. With increasingtemperature, the differences in the viscosities between thecellulose-[BMIm]Cl-10 wt % acetic acid and cellulose-[BMIm]Cl solutionsdiminish and the observed viscosities depend upon the shear rate.

This example shows that the viscosity of a cellulose-ionic liquidsolution can be dramatically altered by adding a miscible cosolvent suchas a carboxylic acid to the solution. The viscosity drops withincreasing miscible cosolvent reaching a minimum before increasing againas addition cosolvent is added.

Example 38 Viscosity of Solutions of Cellulose Dissolved in IonicLiquids Containing Immiscible Cosolvents

To determine the impact of an immiscible cosolvent which, forms twolayers with the initial cellulose-ionic liquid solution, on solutionviscosity it is necessary to convert the cellulose to a cellulose esterprior to making the viscosity measurement.

To a 3-neck 100 mL round bottom flask equipped for mechanical stirringand with an N2/vacuum inlet was added 33.18 g of1-butyl-3-methylimidazolium chloride. While stirring rapidly, added 1.75g of dry cellulose (5 wt %). The flask was placed under vacuum (2 mm Hg)and placed in an oil bath preheated to 80° C. After 30 min in the oilbath all of the cellulose was dissolved. The oil bath and stirring wasturned off and the solution was left under vacuum overnight.

To the cellulose solution was added 30 mL of methyl ethyl ketoneresulting in a 2-phase reaction mixture. While stirring rapidly, added amixture of 104 mg of MSA and 5.51 g of Ac₂O dropwise (3 min). At the endof the addition, the reaction mixture was two phases. After stirring forca. 70 min from the start of addition, the reaction mixture was a singlephase; the viscosity of the phase was much less than that of theoriginal cellulose solution. Stirring was continued for an additional150 min before 10.9 g of the solution was removed for viscositymeasurements. The remaining solution was then cooled to room temperatureand the product was isolated by precipitating in 350 mL of MeOH. Theslurry was stirred for ca. 1 h before the solids were isolated byfiltration. The solids were washed 4 times with 250 mL of MeOH. Thesolids were then dried overnight at 50° C., 5 mm Hg which gave 1.66 g ofa white solid. Analysis revealed that the solid was the expectedcellulose acetate. A second reaction was conducted in the same fashionexcept that the cosolvent was omitted. Again, a sample was removed forviscosity measurements just prior to precipitation of the celluloseacetate.

FIG. 29 compares the solution viscosity of the contact mixtures with andwithout cosolvents at 25° C. Inclusion of a cosolvent dramaticallyreduces the viscosity of the solution. For example at 25° C. and 1rad/sec, inclusion of methyl ethyl ketone resulted in a solution with aviscosity of 24.6 poise versus 6392 poise for the solution withoutmethyl ethyl ketone.

Example 39 Impact of Miscible Cosolvents on Reaction Rates and Total DS

A 3-neck 100 mL round bottom flask was equipped with a double neckadapter giving four ports, an iC10 diamond tipped IR probe, formechanical stirring, and a N₂/vacuum inlet. To the flask was added 50.15g of 1-butyl-3-methylimidazolium propionate ([BMIm]OPr). While stirringrapidly, cellulose (4.07 g, 7.5 wt %) was added to the [BMIm]OPr at roomtemperature. Vacuum was applied with the aid of a bleed valve. Afterreaching 0.6 mm Hg, a preheated 80° C. oil bath was raised to the flask.A clear solution was obtained 8 min after raising the oil bath. Stirringwas continued for an additional 2.8 h before the solution was allowed tocool to room temperature and stand under N₂ for 12 h.

To the cellulose solution at room temperature was added a mixture ofpropionic anhydride (12.09 g, 3.7 eq) and MSA (482 mg, 0.2 eq) dropwise(20 min). During the course of the reaction, aliquots were removed andthe product was isolated by precipitation in 200 mL of MeOH andfiltering. The reaction was complete 20 min after the end of addition.The experiment was terminated and the remaining reaction mixture wasprocessed as the aliquots. The solid from each sample was washed 3 timeswith 200 mL portions of MeOH then 1 time with 250 mL of MeOH containing8 wt % of 35 wt % H₂O₂. The white solids were then dried at 60° C., 5 mmHg.

A second experiment was conducted following the same procedure. The onlydifference was that the [BMIm]OPr contained 11.9 wt % propionic acid asa miscible cosolvent.

FIG. 30 shows a plot of absorbance for a band at 1212 cm⁻¹ (propionateester and propionic acid) versus contact time. The DS indicated in FIG.30 correspond to the DS values for the samples obtained in eachexperiment. Relative to the reaction of cellulose dissolved in [BMIm]OPr(no propionic acid), the reaction rate of cellulose dissolved in[BMIm]OPr+11.9 wt % propionic acid is slower and the DS of each sampleis higher than the corresponding sample in the other experiment. Thus,this example shows in addition to impacting solution viscosity, acosolvent can also have a dramatic impact on reaction rates and total DSobtained.

Example 40 Regioselective Esterification of Cellulose Dissolved in IonicLiquids by the Controlled Addition of Anhydrides

Series 1: A 3-neck 100 mL round bottom flask which contained a solution4.9 g (7.5 wt %) of cellulose dissolved in [BMIm]Cl was equipped formechanical stirring, with an iC10 diamond tipped IR probe, and with anN₂/vacuum inlet. The flask contents were heated to 80° C. before addingmixture of 5.9 g Pr₂O (1.5 eq) and 0.29 g MSA (0.1 eq) to the cellulosesolution (4 min addition). The consumption of anhydride and theproduction of cellulose ester and carboxylic acid was followed in situusing infrared spectroscopy. Forty minutes after the start of the Pr₂Oaddition, 4.66 g of Ac₂O (1.5 eq) was added to the contact mixture (2min addition). The contact mixture was stirred for an additional 2 h at80° C. before adding 1 g of n-propanol to quench the remaininganhydride. During the course and at the end of the contact period, thecontact mixture was sampled by removing 6-10 g aliquots of the contactmixture and cellulose ester was obtained by precipitation in aqueousmethanol. The solid from each aliquot was washed 4× with aqueousmethanol then dried at 60° C., 5 mm Hg.

FIG. 31 is a plot of absorbance versus time for series 1, and itillustrates the esterification of cellulose (1756, 1233, 1212 cm⁻¹), theconsumption of anhydride (1815 cm⁻¹), and the coproduction of carboxylicacid (1706 cm⁻¹) during the experiment. The DS values shown in FIG. 31were determined by proton NMR spectroscopy and correspond to the samplesremoved during the course of the contact period. The change in theacetyl methyl (centered near 1.9 ppm) and propionyl methyl (centerednear 1.0 ppm) resonances (FIG. 32) clearly indicated a nonrandomdistribution of the acyl substituents. This finding is surprising inthat cellulose esters prepared by conventional processes typically havea random distribution of acyl substituents. That is, the relative degreeof substitution at the C₆, C₃, and C₂ anhydroglucose monomer is close toa 1:1:1 ratio.

Series 2: Following the general procedure of series 1, cellulosedissolved in [BMIm]Cl was esterified by first adding a mixture of 1.5 eqAc₂O and 0.1 eq MSA. Twenty minutes after adding the Ac₂O, 1.5 eq Pr₂Owas added to the contact mixture. The contact mixture was stirred for anadditional 7 h at 80° C. As with series 1, during the course and at theend of the contact period, the contact mixture was sampled by removing6-10 g aliquots of the contact mixture and cellulose ester was obtainedby precipitation in aqueous methanol. Proton NMR again indicated anonrandom distribution of the acyl substituents different from thatobtained with series 1.

Series 3: Following the general procedure of series 1, cellulosedissolved in [BMIm]Cl was esterified by adding a mixture of 1.5 eq Ac₂O,1.5 eq Pr₂O, and 0.1 eq MSA. The contact time was 2 h 5 min. As withseries 1 and 2, during the course and at the end of the contact period,the contact mixture was sampled by removing 6-10 g aliquots of thecontact mixture, and cellulose ester was obtained by precipitation inaqueous methanol. Proton NMR again indicated a nonrandom distribution ofthe acyl substituents different from that obtained with series 1 and 2.

In order to measure the differences in RDS obtained by the differentorder of anhydride additions, selected aliquots (400 mg each) from eachsample series was dissolved in pyridine and contacted withp-nitrobenzoyl chloride (1 g) at 70° C. for ca. 23 h beforeprecipitating and washing with EtOH. This process converted thecellulose acetate propionate esters to fully substituted celluloseacetate propionate p-nitrobenzoate esters. These samples were thenanalyzed by carbon 13 NMR, and the RDS could be determined byintegration of the carbonyl resonances. The position of thep-nitrobenzoate esters indicate the location of the hydroxyls in thecellulose acetate propionate. FIG. 33 compares the carbonyl region inthe ¹³C NMR spectra of a sample from each series having a similar DS;the RDS for each sample is given in the Figure.

Examination of the RDS for each series shows that in each case the orderof reactivity is C₆>>C₃>C₂. For example, for series 1 in which thepropionate was added first, RDS C₆=1.00, RDS C₃=0.89, and RDS C₂=0.73.In terms of acetate versus propionate selectivity, the RDS_(Pr) at C₆was 0.78 and the RDS_(Ac) at C₆ was 0.26. Comparing the RDS for acetateversus propionate at C₃ and C₂, it is evident that that there is moreacetate than propionate at C₃ (0.50 versus 0.39) and C₂ (0.47 versus0.26). That is, placement of the acyl substituents was regioselectiveleading to a cellulose acetate propionate enriched in6-propionyl-2,3-diacetyl cellulose. In series 1, the propionate carbonylC₆/C₂ and C₆/C₂ ratios were large (2.0 and 3.0, respectively) as werethe propionate carbonyl C₆/C₃*DS (2.8) and C₆/C₂*DS (4.2) values. In thecase of series 2 in which the Ac₂O was added first, RDS C₆=1.00, RDSC₃=0.93, RDS C₂=0.86. In terms of acetate versus propionate selectivity,the RDS_(Pr) at C₆ was 0.25 and the RDS_(Ac) at C₆ was 0.75 oppositefrom that observed with series 1. In series 2, the acetate carbonylC₆/C₂ and C₆/C₂ ratios were large (1.5 and 2.0, respectively) as werethe acetate carbonyl C₆/C₃*DS (2.3) and C₆/C₂*DS (3.1) values. In thecase of Series 3, in which the Ac₂O and the Pr₂O were added as amixture, regioselectivity was still observed; RDS C₆=1.00, RDS C₃=0.68,RDS C₂=0.50. In terms of acetate versus propionate selectivity, theRDS_(Pr) at C₆ was 0.56 and the RDS_(Ac) at C₆ was 0.44. At C3, the RDSfor propionate and acetate were roughly equivalent. At C₂, the RDS_(Pr)was 0.20 and the RDS_(Ac) was 0.30. In series 3, the propionate carbonylC₆/C₂ and C₆/C₂ ratios were large (1.6 and 2.8, respectively) as werethe propionate carbonyl C₆/C₃*DS (1.7) and C₆/C₂*DS (3.1) values.

Regioselective placement of substituents in a cellulose ester leads topolymers with different physical properties in a fashion analogous toclassical random copolymers versus block copolymers. As an example, FIG.34 shows a plot of DS versus glass transition temperature (Tg) for thepolymers prepared in series 1-3. At a given DS, the Tg for series 1 isshifted 5° C. lower relative to series 2. In turn, the Tg for series 2is shifted 5° C. lower relative to series 3. That is, the Tg can beshifted as much as 10° C. at a constant DS by controlling the placementof the acyl substituents. FIG. 35 shows a plot of DS_(Pr) versus Tg forthe same series 1-3. The slope of the lines for series 2 and 3 aresimilar and are ca. twice that of series 1. This means that when thepropionate substituent is located predominately at C₆, small changes inDS_(Pr) will result in large changes in Tg. This illustrates that thesenew cellulose ester compositions surprisingly leads to polymers havingdifferent and novel physical properties relative to conventionalcellulose ester that impacts their use in many applications.

Example 41 Casting of Film and Film Optical Measurements Using CelluloseEsters Containing a Minor Amount (DS≦0.2) of a Second Acyl Group

Cellulose esters that are essentially 6,3- and 6,2-regioselectivelysubstituted (high C₆ RDS, Examples 41.1-41.3) were prepared according tothe methods of the present invention in Examples 1-3. Commercial(Comparative examples 41.6 and 41.7) cellulose esters available fromEastman Chemical Company, were produced by the general proceduresdescribed in US 2009/0096962 and US 2009/0050842. Comparative examples41.4 and 41.5 were prepared as described in US 2005/0192434. Thecellulose esters in examples 41.4 and 41.5 are essentially2,3-regioselectively substituted and differs from the examples of thepresent invention in that they have a low RDS at C₆ while the celluloseesters of the present invention have a high RDS at C₆. The ring RDS wasdetermined for each sample before film was cast and the film opticalproperties determined. The results are summarized in Table 11.

TABLE 11 The degree of substitution, relative degree of substitution,and out-of- plane retardation (nm) for compensation film for celluloseesters containing a minor amount (DS ≦ 0.2) of a second acyl groupprepared by the methods of the present invention versus comparative (C)cellulose esters. Example IL DS DS_(Pr) DS_(Ac) RDS C₆ RDS C₃ RDS C₂R_(th) (589) 41.1 [EMIm]OAc 2.81 0.00 2.81 1.00 0.86 0.95 −55.9 41.2[BMIm]OPr 2.81 2.77 0.04 1.00 0.86 0.95 36.1 41.3 [BMIm]OPr 1.68 1.650.03 0.85 0.42 0.41 −342.5 41.4 (C) 1.99 1.94 0.05 0.36 0.80 0.83 −80.241.5 (C) 1.53 1.48 0.05 0.24 0.63 0.66 −119.0 41.6 (C) 2.73 2.69 0.040.83 0.98 0.90 −29.2 41.7 (C) 1.93 1.77 0.16 0.56 0.71 0.66 −209.9

Examples 41.1 and 41.2 are essentially identical except that Example41.1 was a cellulose acetate, and Example 41.2 was a cellulosepropionate. As shown in Table 11, the cellulose propionate had a higherR_(th) (+36 nm) relative to the cellulose acetate (−56 nm). Comparingthe values of R_(th) for the low DS 6,3-, 6,2-cellulose propionate(Example 41.3, DS=1.68, C₆/C₃=2.0, C₆/C₂=2.1, DS*C₆/C₃=3.4,DS*C₆/C₂=3.5) to the two 2,3-cellulose propionates (Example 41.4,DS=1.99 C₆/C₃=0.45, C₆/C₂=0.43, DS*C₆/C₃=0.9, DS*C₆/C₂=0.9 and Example41.5, DS=1.53, C₆/C₃=0.38, C₆/C₂=0.36, DS*C₆/C₃=0.6, DS*C₆/C₂=0.6) itwas evident that the 6,3-, 6,2-cellulose propionate provided a much morenegative R_(th) value (−343 nm versus −80 and −119 nm) even though thecellulose esters have similar DS values. Similarly, comparison of theR_(th) value for Example 41.3 to the R_(th) value for Example 41.7(DS=1.93, C₆/C₃=0.79, C₆/C₂=0.85, DS*C₆/C₃=1.5, DS*C₆/C₂=1.6) revealedthat the regioselectively substituted cellulose propionate had a muchlower R_(th) value (−343 nm versus −210 nm). Comparison of the R_(th)value for the high DS regioselectively substituted cellulose propionate(Example 41.2, DS=2.81, C₆/C₃=1.16, C₆/C₂=1.05, DS*C₆/C₃=3.3,DS*C₆/C₂=3.0) to the R_(th) value for the high DS conventional cellulosepropionate (Example 41.6, DS=2.73, C₆/C₃=0.85, C₆/C₂=0.92, DS*C₆/C₃=2.3,DS*C₆/C₂=2.3) revealed that the regioselectively substituted cellulosepropionate has a much higher R_(th) (+36 nm) than the conventionalcellulose propionate (−29 nm).

This example illustrated several important aspects of the presentinvention. As the comparison of Examples 41.1 and 41.2 demonstrated, apropionate substituent increased R_(th) more that an acetate substituentat an equivalent DS and substitution pattern. As expected, the totalhydroxyl DS had a significant influence on the R_(th) values regardlessof the substitution pattern. However, the regioselectively substitutedcellulose esters of the present invention provided for a much widerrange of R_(th) relative to other substitution patterns. At the lower DSrange, R_(th) was much more negative for the regioselectivelysubstituted cellulose esters relative to conventional cellulose esters.At higher DS range, R_(th) was less negative and even positive for theregioselectively substituted cellulose esters relative to othercellulose esters.

Example 42 Casting of Film and Film Optical Measurements Using CelluloseEsters Containing a Second Acyl Group (DS≧0.2)

Regioselectively substituted cellulose acetate propionates (Examples42.1-42.6) were prepared according to the methods of the presentinvention (high C₆ RDS) in Examples 1-6. Comparative example 42.7cellulose ester was a cellulose acetate propionate that was prepared bythe general procedures described in US 2009/0096962 and US 2009/0050842and is available from Eastman Chemical Company. The ring and carbonylRDS were determined for each sample before film was cast, and the filmoptical properties were determined. Table 12 provides the ring RDSversus R_(th), Table 13 provides the carbonyl RDS versus R_(th), andTable 14 provides the propionate and acetate ratios of C₆/C₃ and C₆/C₂as well as C₆/C₃*DS and C₆/C₂*DS.

TABLE 12 The degree of substitution, relative degree of substitution,and out-of-plane retardation (nm) for compensation film for celluloseesters containing a second acyl group (DS ≧ 0.2) prepared by the methodsof the present invention from cellulose dissolved in [BMIm]Cl versuscomparative (C) cellulose esters. Example DS DS_(Pr) DS_(Ac) RDS C₆ RDSC₃ RDS C₂ R_(th) (589) 42.1 1.99 1.15 0.85 1.00 0.62 0.42 −109.5 42.22.14 0.90 1.24 1.00 0.69 0.48 −54.2 42.3 2.34 0.99 1.35 1.00 0.77 0.60−137.2 42.4 2.61 1.41 1.20 1.00 0.89 0.73 −17.4 42.5 2.77 1.25 1.52 1.000.93 0.86 −33.7 42.6 2.17 1.10 1.07 1.00 0.68 0.50 −156.9 42.7 (C) 2.470.88 1.59 0.75 0.90 0.82 −161.7

TABLE 13 The degree of substitution, carbonyl carbon relative degree ofsubstitution, and out-of-plane retardation (nm) for compensation filmfor cellulose propionates prepared from cellulose dissolved in [BMIm]Clby the methods of the present invention versus comparative (C) celluloseesters. Example DS DS_(Pr) DS_(Ac) Pr C₆ Pr C₃ Pr C₂ Ac C₆ Ac C₃ Ac C₂R_(th) (589) 42.1 1.99 1.15 0.85 0.52 0.39 0.24 0.48 0.23 0.18 −109.542.2 2.14 0.90 1.24 0.48 0.28 0.14 0.52 0.41 0.34 −54.2 42.3 2.34 0.991.35 0.56 0.28 0.18 0.44 0.49 0.42 −137.2 42.4 2.61 1.41 1.20 0.78 0.390.26 0.22 0.50 0.47 −17.4 42.5 2.77 1.25 1.52 0.25 0.44 0.49 0.75 0.490.37 −33.7 42.6 2.17 1.10 1.07 0.56 0.36 0.20 0.44 0.32 0.30 −156.9 42.7(C) 2.47 0.88 1.59 0.29 0.26 0.31 0.52 0.53 0.53 −161.7

TABLE 14 The ratios of C₆/C₃ and C₆/C₂ as well as C₆/C₃*DS and C₆/C₂*DSproducts for propionate and acetate and the corresponding Rth values(nm) for compensation film for cellulose acetate propionates preparedfrom cellulose dissolved in [BMIm]Cl by the methods of the presentinvention versus comparative (C) cellulose esters. Pr Pr C₆/C₃* C₆/C₂*Ac Ac C₆/C₃* C₆/C₂* R_(th) Example C₆/C₃ C₆/C₂ DS_(Pr) DS_(Pr) C₆/C₃C₆/C₂ DS_(Ac) DS_(Ac) (589) 42.1 1.33 2.17 1.53 2.49 2.09 2.67 1.77 2.27−109.5 42.2 1.71 3.43 1.54 3.09 1.27 1.53 1.57 1.90 −54.2 42.3 2.00 3.111.98 3.08 0.90 1.05 1.21 1.41 −137.2 42.4 2.00 3.00 2.82 4.23 0.44 0.470.53 0.56 −17.4 42.5 0.57 0.51 0.71 0.64 1.53 2.03 2.33 3.08 −33.7 42.61.56 2.80 1.71 3.08 1.38 1.47 1.47 1.57 −156.9 42.7 (C) 1.12 0.94 0.980.82 0.98 0.98 1.56 1.56 −161.7

Upon comparing Examples 42.1-42.6 to Example 42.7 (Table 12), it isevident that the regioselectively substituted cellulose acetatepropionates gave R_(th) values that were less negative than thatprovided by the conventional cellulose acetate propionate regardless ofDS_(OH). As an illustration, Example 42.3 had a slightly lower DSrelative to Example 42.7, but the R_(th) value of Example 42.3(R_(th)=−137 nm) was still less negative than Example 42.7 (R_(th)=−162nm). Even upon further reduction in total DS (increasing DS_(OH),Examples 42.1, 42.2, and 42.6), the R_(th) values for theregioselectively substituted cellulose acetate propionates were stillless negative.

As Table 12 shows, Examples 42.1-42.6 had high ring RDS C₆/C₃ and C₆/C₂ratios but there was variation in R_(th) at similar total DS values. Asan illustration, Examples 42.6 and 42.2 had similar DS values butsignificantly different R_(th) values (−157 nm versus −54 nm). Uponexamination of the carbonyl RDS C₆/C₃ and C₆/C₂ ratios for these twoExamples, it was evident that Example 42.2 (R_(th)=−54 nm) had a muchhigher C₆/C₃ and C₆/C₂ Pr RDS than did Example 42.6. Similarly, Example42.4 had a lower DS (2.61) than did Example 42.5 (2.77), but yet theR_(th) value for Example 42.4 (−17 nm) was less negative than Example42.5 (−34 nm). Again, examination of the carbonyl RDS C₆/C₃ and C₆/C₂ratios for these two Examples revealed that Example 42.4 had a muchhigher C₆/C₃ and C₆/C₂ Pr RDS than did Example 42.5. That is, havingpropionate at C₆ with a high C₆/C₃ and C₆/C₂ Pr RDS ratios had asignificant influence on R_(th).

In Example 41 (single acyl substituent), it was shown that a propionatesubstituent increased R_(th) more that an acetate substituent at anequivalent DS and substitution pattern and that the total hydroxyl DShad a significant influence on the R_(th) values. The regioselectivelysubstituted cellulose esters provided for a much wider range of R_(th)relative to other substitution patterns. The present Example illustratedthe influence that a second acyl group can have on R_(th) values. Thatis, for regioselectively substituted cellulose esters of the presentinvention, the combination of acetyl and propionyl substituents led to anarrower and less negative R_(th) range relative to conventionalcellulose esters. Higher propionate DS and high C₆/C₃ and C₆/C₂ Pr RDSratios at equivalent total DS served to further modify R_(th).

1. A process of making a regioselectively substituted cellulose estersaid process comprising: (a) introducing a reaction medium comprisingcellulose, a halide ionic liquid and a binary component into anesterification zone; and (b) combining at least one acylating reagentwith said reaction medium in said esterification zone to esterify atleast a portion of said cellulose thereby producing saidregioselectively substituted cellulose ester; wherein said acylatingreagent is added at one time or in consecutive stages.
 2. A processaccording to claim 1 wherein about 80 mole percent of a first acylatingreagent is allowed to react prior to adding the next acylating agent. 3.A process of making a regioselectively substituted cellulose ester saidprocess comprising: (a) dissolving a cellulose in a halide ionic liquidto thereby form an initial cellulose solution; (b) contacting saidinitial cellulose solution with a binary component and an acylatingreagent under conditions sufficient to provide an acylated cellulosesolution comprising a cellulose ester; wherein said acylating reagent isadded at one time or in consecutive stages; (c) contacting said acylatedcellulose solution with a non-solvent to cause at least a portion ofsaid cellulose ester to precipitate and thereby provide a slurrycomprising precipitated cellulose ester and at least a portion of saidhalide ionic liquid; (d) separating at least a portion of saidprecipitated cellulose ester from said halide ionic liquid to therebyprovide a recovered cellulose ester and a separated halide ionic liquid;and (e) optionally, recycling at least a portion of said separatedhalide ionic liquid for use in dissolving additional cellulose.